Price Comparision

Hi all

I am facing problem in price comparision after maintaining Quotations.

I put the collective RFQ number in the initial screen while carrying out T-code ME49.

when i execute in get the message as ""Selected quotations not directly comparable""

I have maintained the prices in maintain quotation, but still i get in the field as ""quotation item not yet maintained "" in ME49.

Can anyone please suggest where am i going wrong and also whether any customiziing has to be carried out.