Error when executing Update Membership Statuses Scheduled Job
I took a look at the code for you, and I couldn't see a stand out problem. The bad news is that you need a developer to look at this, insert debug information (or run it in the debugger) and really figure out what's going on.

Most helpful would be if you requested the logs from your SysAdmin, and then posted back when you have them. We need to figure the path of execution.

Do you have custom extensions installed, and does it work if they are disabled?