Thank you for your reply. I mentioned that this problem was reported in the Tracker system (Bug CORE-5306) and my problem is just the same.
Basically I get the following type of error invalid request BLR at offset 36. function EXTRACTDAY is not defined. module name or entrypoint could not be found. This is on a clean install, no configurtation of Firebird.conf - so whatever the defaults are. It is also on Windows 7 64. The UDFs are in the Firebird/UDF folder. I checked the .conf and the UdfAccess is commented out. I can copy this exact folder across onto a Firebird 2.5 system and it works perfectly. Also with the default installation settings on the same computer. I only have one user on all of my installs and that is SYSDBA.