Replication Agent Failing on First Run

When I first try to run the replication agent, I get a message in the Replic
ation Monitor that says "The Agent is suspect. No response within the last 1
0 minutes."  I tried increasing the Replication Monitor Inactivity Threshold
 to 20 minutes but got the same result.

When I look at the job that is run, there are three steps:
1. Snapshot Agen startup message.
2. Run agent.
3. Detect nonlogged agen shutdown.

Step 1 appears to run successfully.

The job appears to be failing on Step 2. (I tried setting step to quit with 
failure instead of going onto the next step and the whole job failed.

When step 3 does run, I am getting the following output:

Job 'KRONOS-tkcsdb_test-tkcsdb_test-1' : Step 3, 'Detect nonlogged agent shu
tdown.' : Began Executing 2005-04-21 11:49:54

Msg 515, Sev 16: Cannot insert the value NULL into column 'runstatus', table
 'distribution.dbo. MSsnapshot_history';
 column does not allow nulls. INSERT 
fails. [SQLSTATE 23000]
Msg 3621, Sev 16: The statement has been terminated. [SQLSTATE 01000]

I'm new to SQL Server and would greatly appreciate any help.

Thanks.
Greg C.