You are in the wrong DBforum, isql is for Sybase.
Anyway syntax error 201 implies the following,
Procedure %.*s expects parameter %.*s, which was not supplied.
Explanation: Adaptive Server could not perform the requested action. Check your command for missing or incorrect database objects, variable names, and/or input data.
But if you have mistakenly said isql, from the session where you had started the informix, run finderr 201 and see the explanation. Also from dbaccess you can try running your syntax and if it is wrong it will show you where the syntax is wrong.