A recent CentOS update is evidently causing issues with the plesk daemon. I ran afoul of it when I discovered that plesk would not start up after being shut down.
The daemon will be running fine, but will break on the next restart. I imagine this may affect all plesk servers until plesk pushes out the update from their end.
Signs of issue:
2010-03-29 11:31:29: (log.c.75) server started
2010-03-29 11:31:29: (network.c.336) SSL: error:00000000:lib(0):func(0):reason(0)
Relevant Plesk KB link with fix: