My Business Visa is rejected stating Duly Authorized Invitation Letter not available.

Sachin, perhaps the officer wants you to submit an invitation letter or invitation confirmation letter from a duly authorized unit (e.g: the chamber of commerce or organizations authorized by the Foreign Affairs Ministry). You should first find out the reson for being rejected by contacting the CVASC center, then wait for a time, and reapply for the M type with the duly authorized invitation letter.