Sales Order Against Contract

Hi,

When we create Sales Order with reference to Contract and if Qty exceeded in Sales order against the Contract qty, system is giving warning message as under -

Target qty of reference: 1.000 TO (total referenced: 2.000 TO) Message no. V1501

We want to convert this warning message in error message.

Please inform how can we convert the message in error.

Regards,

Vinay