Datawindow Error: ct_describe(): user api layer: external error

Hi,

In my application using Powerbuilder 12.5 and sybase 15.

While running my application, In some occassions i am getting this below error message.

"Select error: ct_describe(): user api layer: external error : An

illegal value of 4 given for parameter item."

i don't understand the above error message.Please suggest upon this.!

Thanks,

Krishna.