Sql Server 2008r2 Replication Snapshot Agent Hang

I am setting up a new merge publication, but I can not get the snapshot agent to run successfully. In fact, I can not run any snapshot agents for any of the other publications on this server now. This is effecting transactional and merge publications

When running a snapshot, I get the "Starting agent." status returned and then the occasional "agent has not logged a message in 10 minutes" messages.

I've also tried generating a snapshot from the command line:

I never get any errors nor is the c:\repllog.txt log file ever created. It feels like something mysterious is blocking the snapshot executable pretty much on start up. Any ideas?