First I am assuming you did not change the title line for the aircraft as that would normally give a "can't find" error. My suspicion then is a blank space where one should not be
Since you have opened and read one, try comparing yours to mine which works perfectly for me. Alternatively, you could copy mine and paste it into a new text file and rename that PA23-1 Minnesota Summer.FLT and substitute it for your non-working flt.
-----------------------
[Main]
Title=PA23-1 Minnesota Summer
Description=There is a light breeze from the South so take off and get familiar with the area. Do some touch and goes from both directions and splash some water up from the mud puddle..
)
AppVersion=9.0.30612
FlightVersion=1
[Tower]
Latitude=N046° 58' 56.2201"
Longitude=W091° 48' 30.6289"
Altitude=+000932.00
[Track]
Latitude=N047° 25' 53.4256"
Longitude=W122° 18' 28.7933"
Altitude=+000432.00
[Options]
Titles=False
Sound=True
Pause=False
AxisIndicator=Off
ATC=False
Moonlight=True
SimSpeed=001.00
ShowStars=True
ApproachLights=True
FlightDisplay=Off
SlewDisplay=Coordinates
[EFIS]
Active=False
Type=Rectangles
Density=Thin
Range=Short
NavAid=VOR 1
Altitude=0
Flags=0
[Avionics]
LocalizerSelect=Auto Select
DMESelect=1
[Kneeboard]
PageId=0
Visible=False
Location=224, 137
Page0Scroll=0, 0
Page1Scroll=0, 0
Page2Scroll=0, 0
Page3Scroll=0, 0
Page4Scroll=0, 0
Page5Scroll=0, 0
[Panels]
Panel.On=True
HUD.On=False
[Window.1]
Order=0
Active=True
Undocked=False
Maximized=True
ScreenUniCoords=0, 0, 8192, 5600
UndocCoords=0, 0, 0, 0
ViewMode=Spot
ViewDir=Forward
CockpitZoom=001.00
VirtualZoom=001.00
TowerZoom=001.00
TrackZoom=004.00
SpotZoom=001.00
MapZoom=011.00
SpotDirection=136.11
SpotDistance=+000077
SpotTransitionType=Fixed
SpotFastTransition=False
SpotAltitude=-000006
PanHeading=360.00
PanPitch=360.00
PanBank=360.00
ChaseTarget=1
SavedViewMode=Tower
[ATC_AgentManager]
NumberofAgents=0
[ATC_Aircraft.0]
ActiveFlightPlan=False
RequestedFlightPlan=False
AcState=ACSTATE_REQUEST_TAXI_CLEARANCE_OUT_VFR_ATIS
NumberofWaypoints=0
ClearanceFlags=80
CtCur=CLEARANCE_NONE
WaypointNext=0
AltCleared=-1
HdgAssigned=-1
SquawkAssigned=1072697856
LandingSequence=LANDING_NONE
DepartureRequest=DEPARTURE_VFR_REQUEST_NONE
ParkingRequest=PARKING_NAME_NONE
PatternLeg=PATTERN_LEG_NONE
ApproachIndex=-1
ApproachTransitionIndex=-1
ApproachRequestIndex=-1
ApproachTransitionRequestIndex=-1
RunwayIndex=-1
RunwayRequestIndex=-1
ParkingIndex=-1
FlightFollowing=FLIGHT_FOLLOWING_NO
AirspaceTransition=AIRSPACE_TRANSITION_NONE
BVAirspaceTransition=BV_TYPE_NONE
BVAirspaceTransitionReq=BV_TYPE_NONE
TakeoffSequence=TAKEOFF_SEQUENCE_NONE
LandingSequenceNumber=-1
TaxiRouteCurrent=-1
CruisingAltitude=-1
RequestedCruisingAltitude=-1
ExpectedAltitude=-1
AircraftSignature=1,0
[ATC_AircraftManager]
NumberofAircraft=1
[ATC_MessageSystem]
FrequencyNodes=0
[DateTimeSeason]
Day=237
Year=2003
Hours=10
Minutes=8
Seconds=9
Season=Summer
[Panel.1]
ScreenUniCoords=0, 0, 8192, 6144
UndocCoords=0, 0, 0, 0
Visible=False
Undocked=False
HiddenOn=False
ID=0
ViewsOn=1
[Panel.2]
ScreenUniCoords=0, 0, 8192, 6144
UndocCoords=0, 0, 0, 0
Visible=False
Undocked=False
HiddenOn=False
ID=-1
ViewsOn=1
[Panel.3]
ScreenUniCoords=0, 0, 0, 0
UndocCoords=0, 0, 0, 0
Visible=False
Undocked=False
HiddenOn=False
ID=10
ViewsOn=0
[Panel.4]
ScreenUniCoords=0, 0, 0, 0
UndocCoords=0, 0, 0, 0
Visible=False
Undocked=False
HiddenOn=False
ID=225
ViewsOn=0
[Gauges]
Airspeed=Operative
TurnCoordinator=Operative
DG=Operative
Altimeter=Operative
AI=Operative
VSI=Operative
Comm=Operative
Nav=Operative
Transponder=Operative
ADF=Operative
Compass=Operative
PitotSystem=Operative
VacuumSystem=Operative
Fuel=Operative
Engine=Operative
Electrical=Operative
PanelLights=False
[Slew.0]
Active=False
[Plane.0]
Aircraft=Piper Apache Red/Cream
[SimVars.0]
Latitude=N046° 58' 56.5034"
Longitude=W091° 48' 29.7485"
Altitude=+000951.62
Pitch=-2.2567640130808817
Bank=-0.21723898717105225
Heading=89.774837872406593
PVelBodyAxis=0
BVelBodyAxis=0
HVelBodyAxis=0
XVelBodyAxis=0
YVelBodyAxis=0
ZVelBodyAxis=0
DynPres=0.0038853962144548781
AGL=3.4439844798412027
SimOnGround=True
PAccBodyAxis=0.053714628488547508
BAccBodyAxis=0.010252352445374731
HAccBodyAxis=-0.00051601258563163763
XAccBodyAxis=0.13064118031404409
YAccBodyAxis=-0.58752940324104941
ZAccBodyAxis=-0.024364454608757802
PVelWorld=0
BVelWorld=0
HVelWorld=0
XVelWorld=0
YVelWorld=0
ZVelWorld=0
IceAccum=0
AutoFeatherSwitch=False
MaximumGForce=1.7030086297941458
MinimumGForce=0.28893604977272974
[Engine Parameters.1.0]
ThrottleLeverPct=0.005828857421875
PropellerLeverPct=1
MixtureLeverPct=0
Pct Engine RPM=0
MaxReachedEngineRPM=0
LeftMagneto=False
RightMagneto=False
GeneratorSwitch=False
CowlFlapPct=1
FuelPumpSwitch=True
CarbHeat/DeiceSwitch=False
[Engine Parameters.2.0]
ThrottleLeverPct=0.005828857421875
PropellerLeverPct=1
MixtureLeverPct=0
Pct Engine RPM=0
MaxReachedEngineRPM=0
LeftMagneto=False
RightMagneto=False
GeneratorSwitch=False
CowlFlapPct=1
FuelPumpSwitch=True
CarbHeat/DeiceSwitch=False
[Fuel.0]
TankSelector=All
TankSelector1=All
Center=100
LeftMain=94.880777280332083
RightMain=94.880777280332083
LeftAux=100
RightAux=100
LeftTip=100
RightTip=100
Center 2=100
Center 3=100
External 1=100
External 2=100
[Controls.0]
SpoilersHandle=000.00
LeftSpoiler=000.00
RightSpoiler=000.00
FlapsHandle=000.00
LeftFlap=000.00
RightFlap=000.00
GearsHandle=100.00
Gear1=100.00
Gear2=100.00
Gear3=100.00
YokeY=050.00
YokeX=050.00
Rudder=050.00
LeftBrake=100.00
RightBrake=100.00
ParkingBrake=100.00
ElevatorTrim=050.00
RudderTrim=0
AileronTrim=0
[Systems.0]
BatterySwitch=False
AvionicsSwitch=True
StructuralDeiceSwitch=False
PropDeiceSwitch=False
Autobrakes=Off
StandbyVacuum=False
PropSync=False
FlightDirector=False
[Gauges.0]
KollsmanSetting=29.920000076293945
[Switches.0]
PitotHeat=False
BeaconLights=False
LandingLights=False
LogoLights=False
NavLights=False
PanelLights=False
RecognitionLights=False
StrobeLights=False
TaxiLights=False
WingLights=False
CabinLights=False
[Avionics.0]
Comm1Active=122.950
Comm1Standby=118.000
Comm2Active=119.900
Comm2Standby=121.700
Nav1Active=110.30
Nav1Standby=110.60
OBS1=340
Nav2Active=116.80
Nav2Standby=109.60
OBS2=315
Transponder=1200
ADFActive=353
ADF2Active=281
ComTransmit=1
ComReceiveBoth=False
AudioNav1Listen=False
AudioNav2Listen=False
AudioMarkerListen=False
AudioDmeListen=False
AudioAdfListen=False
AudioAdf2Listen=False
[AutoPilot.0]
MasterSwitch=False
WingLeveler=False
Nav1Lock=False
HeadingLock=False
HeadingValue=340
AltitudeLock=False
AltitudeValue=0
AttitudeHold=False
AirspeedHold=False
AirspeedValue=0
MachHold=False
MachValue=0
VerticalSpeedHold=False
VerticalSpeedValue=0
RPMHold=False
RPMValue=0
GlideslopeHold=False
ApproachHold=False
BackCourseHold=False
YawDamper=False
ToGa=False
AutoThrottleArm=False
GPSdrivesNAV1=False
IsUsedForLesson=False
[Payload.0]
PayloadList=-1
[SimScheduler]
SimTime=13782.469405152209
[Weather]
WeatherType=2
[Air Traffic Control]
Undocked=False
ScreenUniCoords=1500, 1200, 5192, 2000
UndocCoords=0, 0, 0, 0
[Flying Tip]
Undocked=False
ScreenUniCoords=500, 400, 7192, 650
UndocCoords=0, 0, 0, 0