Make sure the user you are using to connect to the database has permissions to that stored procedure. Also, depending on the version of SQL you are using make sure that you're using the correct owner/schema to call the stored procedure if it's needed.

I.E. in 2000 and the owner is not DBO or the user callign the procedure you must specify the owner Exec owninguser.myprocedure

in 2005+ make sure you are specifying the schema if it's not in the default schema of the user attempting to execute the procedure.

-Luke.