Hallo, I have same problem too. I must reinstall my system windows and FS2004. Now when I choose iFly 737, gauge window says I need to install FSUIPC 3.72 or higher or your FSUIPC key is illegal.
FSUIPC.LOG file:
********* FSUIPC, Version 3.999z8 by Pete Dowson *********
Running on Windows Version 5.1 Build 2600 Service Pack 2
Running inside FS2004 (FS9.1 CONTROLS.DLL, FS9.1 WEATHER.DLL)
User Name="Vladimir Mizik"
User Addr="vladotcf@gmail.com"
FSUIPC Key is provided
WIDEFS not user registered, or expired
Module base=61000000
WeatherReadInterval=4
LogOptions=00000001
DebugStatus=15
688 System time = 05/08/2017 19:45:17
688 C:\FS9\
688 System time = 05/08/2017 19:45:17, FS2004 time = 12:00:00 (00:00Z)
29188 FLIGHTS\OTHER\FLTSIM.flt
29203 AIRCRAFT\c172\Cessna172SP.air
29203 Aircraft="Cessna Skyhawk 172SP"
56938 AIRCRAFT\iFly 737-800\iFly737_800_26k.air
56938 Aircraft="iFly 737-800 (Wide screen)"
67656 C:\Users\Adik Kayka\Documents\Flight Simulator Files\UI generated flight.flt
69391 Clear All Weather requested: external weather discarded
69969 Advanced Weather Interface Enabled
113656 WeatherOptions set, now 60047709 (timer=0)
185797 C:\Users\Adik Kayka\Documents\Flight Simulator Files\UI generated flight.flt
187766 Clear All Weather requested: external weather discarded
200563 System time = 05/08/2017 19:48:36, FS2004 time = 12:38:38 (10:38Z)
200563 *** FSUIPC log file being closed
Memory managed: 0 Allocs, 5580 Freed
********* FSUIPC Log file closed *** *******
Simarket
FSUIPC
Order Status: Completed
Order Date: 2016-06-12 14:12:00
Data removed. !! PLEASE NEVER SEND CUSTOMER DATA !!
Thank You for Your help.
Sincerelly, Vladimir.