An existing connection was forcibly closed

Hi,

I'm using DS 4.0 SP3.

My daily job until last thursday worked correctly, but last three days I've got below error:

ODBC data source <LPPLSQLCL0002\LPPLSQLCL0001> error message for operation <SQLFetchScroll>: <[Microsoft][SQL Server Native

  Client 10.0]TCP Provider: An existing connection was forcibly closed by the remote host.

This happened almost at the same time: 4am - 5am but every time in diffrent workflow.

I've checked log of the server where DS is isntalled and I haven't found any error.

I've checked with administrator the log of sql server 2008 also and there was no information of error.

Do you have any idea where is the problem and what else can I check?

Regards