> I am using Firebird-2.5.0.24118-0 on a windows 2003 server and when I try to compile a trigger that contains greek characters in strings i.e between single quotes ('') I get a "Malformed string" error message, no matter of the client program I am using and the compilation fails.

Check that connection charset allows Greek characters. Or, if you
have it set to NONE - encode your trigger creation script into UTF8.

SY, SD.