Std. error in the Module pool program

Hi,

I have created the table control in the module pool program.

In one of the fileds of table control the quntity filed, is getting the standard SAP error.

i.e when i ma entring any value it will get the new value on the screen but once again if i remove that value and try to save it as the blank its giving error "Cannot reset the entry".

Kindly advise.

ASAP.

Thanks.

Joshi