Hello Pete, 
I just registered my FSUIPC with a purchased product key but my PFD in the iFly 737 says "you need to install FSUIPC 3.72 or higher or your FSUIPC's key is illegal" My information is as follows: 
Order#965619 
Here is my Log File: 
********* FSUIPC, Version 3.999y3 by Pete Dowson ********* 
Running on Windows Version 5.1 Build 2600 Service Pack 2 
Verifying Certificate for "C:\FS2004\MODULES\FSUIPC.dll" now ... 
   SUCCESS! Signature verifies okay! 
Running inside FS2004 (FS9.1 CONTROLS.DLL, FS9.1 WEATHER.DLL) 
User Name="Christopher Maddox" 
User Addr="*******@yahoo.com" 
FSUIPC Key is provided 
WIDEFS not user registered, or expired 
Module base=61000000 
WeatherReadInterval=4 
LogOptions=00000001 
DebugStatus=15 
      484 System time = 27/01/2013 14:41:23 
      484 C:\FS2004\ 
      484 System time = 27/01/2013 14:41:23, FS2004 time = 12:00:00 (00:00Z) 
     4477 C:\Users\Chris Maddox\Documents\Flight Simulator Files\Ohaire Ground.flt 
     4524 AIRCRAFT\iFly 737-700\iFly737_700_26k.air 
     4524 Aircraft="Delta 1" 
    10031 C:\Users\Chris Maddox\Documents\Flight Simulator Files\UI generated flight.flt 
    10842 Clear All Weather requested: external weather discarded 
    11466 Advanced Weather Interface Enabled 
    64662 WeatherOptions set, now 400C3605 (timer=0) 
   952168 System time = 27/01/2013 14:57:15, FS2004 time = 14:41:58 (20:41Z) 
   952168 *** FSUIPC log file being closed 
Memory managed: 0 Allocs, 32393 Freed 
********* FSUIPC Log file closed *** *******