Solved de error message problem! The language was the problem, I was using the cpanel in portuguese so I had to change the line 57 from:
if ((strpos($cbsreturn, "successfully modified")) and (!strpos($cbsreturn, "result in failure"))) {
to
if ((strpos($cbsreturn, "modificado con sucesso")) and (!strpos($cbsreturn, "result in failure"))) {
The "result in failure" is the same, using it in any language.
But couldn't deal with the change quota. Now It works perfectly to change the password, but when I do it, the quota for the account is set to "none".
Thanks again.