session/login issue

Hi all: I inherited an application using PHP 5.1.4 with MySQL 4.1.20, Apache/2.0.46 (Red Hat) on a VPS server with Plesk 7.5. The authentication used to work just fine till yesterday. Now it doesn't authenticate anymore. My debugging so far hasn't revelaed much. It seems like the sessions are not started or started and destroyed right away again. Session handling is done via session class with session data stored in the database. The database doesn't contain any data but debugging revealed that session data is written to the DB and then immediately deleted. None application of the code has changed. Haven't had a chance yet to find out if the hosting company changed/updated anything. I suspect it has something to do with the environment but at the moment I am spinning wheels. Any pointers would be appreciated! Thanks, Gunter