>>isql.exe -database

BG4WS0531:D:\RiTEQFireBird\FB_Backup\TIMETEQ-FIREBIRD-28082011-CLEAN.fdb
-user 'sysdba' -password 'masterke' -i
c:\Scripts\spLabourBudget_Assign.sql;

>>while executing the script I am getting "Unable to open c:\Scripts\spLabourBudget_Assign.sql;" , please guide me why I am getting this error though the file and path name is correct.

It's a DOS command, so you shouldn't have a semi colon at the end ;-)