The error message "Access to UDF library <lib name> is denied by
server administrator" returned by Firebird V1.5.0.4290 can be very
misleading. In addition to what it says this error can also mean that
the UDF library was not found and it can even mean that another
library that is used by the UDF library cannot be found.

I kept getting this error for a UDF library on a test server on which
I restored a copy of a production server/database even so the UDF
library, which was developed by us, existed in the right location with
the right access permissions because these were copied from the
production server. Only when I tried to re-build the UDF library on
the test server I realised that the library libgds.so that is linked
in by our own UDF library could not be found. This was down to a
symbolic link missing from /usr/lib/libgds.so to
firebird/lib/libfbembed.so.

So if you get this error and you are sure that the UDF library exists
in the correct folder and the access permissions are correct then
check the dependencies of that UDF library.

Gerald Krafft
Porism Limited