Lotus notes Intergration with Visual Studio

Hi All,

We currently have an application in VB 6.0 to integrate with Lotus notes 
domino server to read all the do***ent on the server , Lock the do***ents 
from backend to stop the front end users from editing while processing,
and 
go through some processing steps and then save the do***ents with some
edits 
to them and release the do***ent lock which was put earlier.

We are trying to upgrade our software from VB 6.0 to Visual Studio 2008, 
above mentioned functionality is not working in Visual Studio 2008. Its 
working fine if we do not lock the do***ents, but if we lock the
do***ents, 
its reading  all the properties of the lotus notes do***ents and going 
through our normal processing but not able to save the do***ent while its 
locked. Its throwing out an error 

"Notes error: Database already contains a do***ent with this ID (UNID)"

Can someone help me here ?