You didn't mention what version of Data Protector, or what the OS-type of teh cell manager is, so, I can't be real specific
Edit the 'global' file on the cell maanger, and find this line
# SmPeerID=WaitForInMinutes
Description of variable:
# default: 5 minutes
# This timeout is used by all Session Managers
# (BSM/RSM/MSM/DBSM). If the new connection was established to
# the Session Manager (for example: the started
# Disk Agent/Media Agent has connected to SM, new monitor
# (xomnimonitor/omnistat) has connected to SM...) the connected
# client should identify (send its name and version) itself to
# the Session Manager in the specified time. If the client does
# not identify itself in the specified time, SM closes
# connection to the client.
Make a copy of this line, , and edit either one of the lines to remove the # sign and the 'space' that follows, and set the value to 10 minutes
SmPeerID=10
# SmPeerID=WaitForInMinutes
Save the file, stop and restart DP
Don't make the value any larger than 10, if something else is causing this, then all giving the varaible a larger value will do is increase the amount of time it takes to time out