Odk briefcase exporting problem

Hi,
I am using odk aggregate 1.4.5. The odk briefcae displays this message
after the 1600 instances . Can someone help me to solve this problem?

SUBMISSION NOT RETRIEVED: Error fetching submission uri:
uuid:935b1e37-eedc-4995-a52f-45e705abe742 details: Invalid use of
SingleClientConnManager: connection still allocated.
Make sure to release the connection before allocating another one.
fetching instance 1600 ...
SUBMISSION NOT RETRIEVED: Error fetching submission uri:
uuid:f715838d-4caf-4af1-9c93-c628ff546f91 details: Invalid use of
SingleClientConnManager: connection still allocated.
Make sure to release the connection before allocating another one.
retrieving next chunk of instances from server...