Hi Siraj
It seems the 1st line is posted with in SAP, and hence system is able to show you the FI doc..
And is the 2nd line posted from IDOC? The message says it cant show you the IDOC no, whereas you want to see the FI doc no, I guess
Open the CO doc from KSB5 and see if you can branch to the FI doc, using some ref no or something else
Br, Ajay M