Addon Managers For
Flight Simulator
and Prepar3D

Addit! Pro For Prepar3D

I have tried everything but the program just won't install. Any other ideas?

The following procedure should ensure a valid installation of Addit! Pro on all but the most troublesome systems. Be sure to complete every step in the order listed.

Updating your system

1.  Download and install the latest patches, security fixes and service packs for your operating system ( Microsoft often updates core system files in these patches, hotfixes and service packs so it is vital to stay up-to-date.
2.  Download and install the latest patches and updates for your other software (especially those programs that load automatically when you start Windows).
3.  Download and install the latest Visual Basic Run-time files (
4.  Check your hard drive(s) for errors.Using Windows Explorer, open My Computer, right click on your hard drive, pick Properties, move to the Tools tab and under Error Check, click Check Now.
5.  Defragment your hard drive. The latest versions of Windows include a feature that reorganizes program files to speed up execution, which might cause problems. Using Windows Explorer, open My Computer, right click on your hard drive, pick Properties, move to the Tools tab and under Defragmentation, click Defragment Now.
6.  Examine all DLL, OCX and TLB files in your \Windows\System folder (\Windows\System32 folder for Windows 2000/XP users). If any are marked read-only, disable the read-only attribute. If any have a size of 0 bytes, delete them.
7.  Search your hard drive(s) for a file called dao350.dll. Multiple instances of this file can cause problems. You should have one dao350.dll file in your common DAO folder (e.g. "C:\Program Files\Common Files\Microsoft Shared\Dao"). This file should be version 3.51.1608.0 or higher. If you have another copy of this file in other folders, rename or delete them.

Database update for very old systems (this step is optional)
1.  If Addit! Pro is having trouble accessing its database or if you are experiencing problems with Microsoft Jet, DAO or DCOM, download and install DCOM98 for Windows 98, version 1.3 ( There is no direct download for Windows 2000 or XP because DCOM is preinstalled on these operating systems.

Uninstall Addit! Pro

1.  Use Add/Remove Programs to uninstall Addit! Pro.
2.  Use Windows Explorer to delete any leftover Addit! Pro folders and files.
3.  Delete your current Addit! Pro zip archive (it could be corrupt). 
4.  Download a fresh copy of Addit! Pro from (

Prepare to reinstall Addit! Pro

1.  Restart Windows. This is important. You want to start fresh with few or no file locks.
2.  Use Windows Explorer to delete all temporary files and folders from your \Windows\Temp folder.
3.  Windows 2000/XP users should also delete all temporary files and folders from:
     C:\Documents and Settings\Default User\Local Settings\Temp
     C:\Documents and Settings\[your Windows XP user name]\Local Settings\Temp
     If Windows complains some files are in use, just deselect those files and continue to delete what you can. Make absolutely sure you delete the folder msftqws.pdw if present.
4.  Empty the Windows Recycle Bin.
5.  Windows XP users should also run Disk Cleanup. Press the Start button and under All Programs click Accessories then System Tools then pick Disk Cleanup. Select the drive that holds your operating system (usually C:) then press OK and follow the instructions.

Reinstall Addit! Pro

1.  Press CONTROL-ALT-DEL to bring up the Windows task list. Use End Task to remove unneeded programs, especially Cleansweep and virus scanners. For Windows 98, the two to keep are Explorer and Systray. For Windows XP, go to the Applications tab and use End Task on anything not essential. Also go to the Processes tab, sort by user name and use End Process on any User item that's not essential.
2.  Use Windows Explorer to create a new folder on your C: drive called "C:\IAP". Be sure to use this short folder name!
3.  Use an unzipping utility like Winzip ( to extract the contents of the Addit! Pro zip file into "C:\IAP". Do not install at this point, simply extract the files. You should end up with at least these files:
       apfs2004.msi (or apfs2002.msi)*
     Readme.doc (or Readme.htm)
     Register.doc (or Register.htm)
     Whatsnew.txt (or Whatsnew.htm)
     * these files are required for a successful installation!
4.  Use Windows Explorer to run "C:\IAP\Setup.exe". Do not use any other program (including Winzip's Install function) to run the Setup program.
5.  If Setup needs to restart your system and consequently fails to update your system files, make sure your \Windows\Temp folder (C:\Documents and Settings\[your Windows XP user name]\Local Settings\Temp folder for Windows XP users) is not in a RAM drive. Also make sure no utility is clearing the Temp folder on startup (like Winboost).