Deploys have stopped working for one environment

Today, deploys to our test environment have suddenly stopped working. When I got to work this morning, a couple of jobs from this night were stuck in the queue. When I canceled them and retried, I now get an error instead.

I get the same error for all the projects I try:
2013-07-18 06:14:18 INFO Calling PowerShell script: xxx\PostDeploy.ps1’
2013-07-18 06:14:18 ERROR System.ArgumentNullException: String reference not set to an instance of a String.
Parameter name: s
at System.Text.Encoding.GetBytes(String s)

I have tried redeploying previously successfull releases, and get the same error. If I try the same ting in our preprod environment, it works fine. I have tried rebooting the target server. We are running version

I reinstalled the tentacle on the test environment, and now it works again. Case closed (but I have no idea why it stopped working).