How to test inbound webservice with attachment in siebel

Before making IC make sure that the BC class should be "CSSBCFile"
Then In XML request please make sure that the values are

                         FileAutoUpdFlg = Y
                         FileDeferFlg = R
                         QuoteFileDockReqFlg = N
                        QuoteFileDockStatFlg = E

then specify your file name & encoded format.

to get 64bit decoded value of a file, please use this site.