Another info:
Actually interbase shows me that the metadata of the function was
changed to

DECLARE EXTERNAL FUNCTION F_STRBLOB
CSTRING(254) CHARACTER SET NONE
RETURNS BLOB
ENTRY_POINT 'StrBlob' MODULE_NAME 'FreeUDFLib.dll';

So I really would expect it to accept 1 parameter (string) and return
a BLOB

Mirco