Disc Base is not changing automatically when changed Amount while create Invoice "Post with Reference"

Dear Experts,

When I create Invoice tcode FB60 using Post With Reference all the information of the document referred will copy but if I change the value of Amount the field Disc. base amount should change automatically as per the value in Amount field and tax code but in our system it saves as it is just by giving warning message as "Cash discount base exceeds amount posted; correct" please let me know if there is any settings in configuration to fix this.

I have attached the screen shot by marking the fields in red color.

Thanks in advance...

Best Regards

Venkat