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The version of gridex20.ocx library that is distributed with the program has been shrunk with shrinker and it is not compatible with Data Execution Prevention in Windows XP SP2. Data Execution Prevention is a virus protection system in Windows.
The solution is to replace the gridex20.ocx library with the newer version. You can download the new version of the file from this location:
http://www.postcastserver.com/pub/gridex20.zip
Unpack the zip file and copy the gridex20.ocx file into the program's main folder.
Press Start/Run and register the file using the following command:
regsvr32 "c:\program files\postcast server professional\gridex20.ocx"
If the program is installed into a non-default directory on your hard disk, change the path above accordingly.