Replication Log Reader stopped unexpectedly

This morning our websites stopped serving pages.  Whilst investigating I notice that the Replication Sql LogReader had stopped running and was reporting the error:

"SubSystem Message - Job 'XXX582060-XXXXX-1' (0x6D6877EFE4F8EA4D930F8C967FE49BE5), step 2 - A time out occurred while waiting for memory resources to execute the query. Rerun the query."

I have restarted the LogReader and it seems to be working fine but I'd really like to get to the bottom of why it stopped in the first place so I can prevent happening in the future.

Any help would be great.

Thanks

Mike