Is SPTimer Running?
What domain credentials is it running as?

Go into Services from the Control panel and find Windows SharePoint
Timer. If it is running, you may want to even restart it and see if it
starts the job.

What does your event log say?

Also try the command:

net start SPAdmin

That is odd, i'm having the same issue. I have tried all of the commands
suggested below, but the results are the same. I'm using a local account with
admin access to the server.

Here are the error messages i'm seeing:

There is already an object named 'LookupItems_ID_PK' in the database. Could not
create constraint. See previous errors. at
System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean
breakConnection) at
System.Data.SqlClient.SqlInternalConnection.OnError(SqlException exception,
Boolean breakConnection) at
System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject
stateObj) at System.Data.SqlClient.TdsParser.Run(RunBehavior runBehavior,
SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet
bulkCopyHandler, TdsParserStateObject stateObj) at
System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds(String methodName,
Boolean async) at
System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(DbAsyncResult result,
String methodName, Boolean sendToPipe) at
System.Data.SqlClient.SqlCommand.ExecuteNonQuery() at
Microsoft.SharePoint.Utilities.SqlSession.ExecuteNonQuery(SqlCommand command) at
Microsoft.SharePoint.Deployment.SPExport.SerializeLookupListMap() at
Microsoft.SharePoint.Deployment.SPExport.SerializeSettings() at
Microsoft.SharePoint.Deployment.SPExport.Run()

The changeToken refers to a time  before the start of the current change log. at
Microsoft.SharePoint.Deployment.SPExport.ThrowInvalidChangeTokenError(DateTime
minChangeTime, Int32 minChangeNumber) at
Microsoft.SharePoint.Deployment.SPExport.GetIncrementalChanges() at
Microsoft.SharePoint.Deployment.SPExport.CalculateObjectsToExport() at
Microsoft.SharePoint.Deployment.SPExport.Run()


Any ideas on a possible cause?

Did a solution  deployment/feature activation fail in the middle, leaving
remnants behind that are now considered duplicate?

The last content deployment was about a month ago, and succeeded. All of the
features that have been activated have been running since the environment was
setup, and i'm the only one with access to the servers, so additional changes
are not likely. Is there anyway to clear out any leftovers from past jobs that
may be causing problems?

Are you up to date with all your patches? Daylight savings used to end
on the last Sunday in October, which was two days ago...

And discussions that I have seen today seem to indicate that the patches
may have only "fixed" the new start times for daylight savings.

I have not seen a definitive answer on this, but we had some solution
deployments go flaky yesterday and so did others on the boards.