Hi Nisha,
Valuation class does not necessarily cause issue in billing document.
I doubt if the issue is on on sales side, it's most probabaly on purchasing side. Please check in Tcode MM03 for the material, Tab Accounting1 .Check if the caluation class is maintained there. If yes then check table T030 for GL mapping to the valuation class, for specific valuation group code & account modification key.
Regards,
AA