Try adding a space between the connection string and file (e.g. put a space before the @\FILELOCATION\SQLFILENAME.sql
).
call sqlplus UNAME/PASSWD@DBNAME @\FILELOCATION\SQLFILENAME.sql
The other thing to try is to fully qualify your DBNAME. You can look in your tnsnames.ora file (check your Oracle installation folder, and then go to the network\admin folder to find the tnsnames.ora). In there, search for the DBNAME you're trying to connect to, and see what the full name of it is.
(ex: DBNAME.SRV.YOURCOMPANY.COM would be an example).