Lots of Errors, Sudden

[Hall of Famer]

Well first of all, was ACP working for you before? Does this error just pop out right now? And if you dont mind me being curious, Nieth and Clessidra are running the same site?

I am not able to reproduce this error from two of my demo sites, it is not a programming error. Instead, it seems that your server is not able to delete session temp files properly. For this reason its getting full, and thus no space left to write new session data. Here is a reference to the problem encountered by some people:
http://www.webhostingtalk.com/showthread.php?t=681183

You have two options. You may ask your host to install tmpwatch utility, which gets rid of garbage session data automatically. Or you may request the php ini file setting to be changed for the following three parameters:

Originally Posted by checklist

session.gc_probability "1" PHP_INI_ALL
session.gc_divisor "100" PHP_INI_ALL
session.gc_maxlifetime "1440" PHP_INI_ALL

If the session.gc_probability or session.gc_divisor has value 0 in your server php.ini file, you are likely to have a problem. If session.gc_maxlifetime is too long, it will slow down the process of getting rid of junk session data too. This is something only your host can fix, and I dont see why they wont. Contact them and see if there's anything that can be done. You need to fix this though even if you dont use ACP, it is not the only place that writes session data.