What causes my /dev/hda2 to remount in read only mode?
 

Anyone knowing the reason why our /dev/hda2 partition remounts read only after a while up running.

We're running Debian 3.0r2, filesystem is ext2 @ work.
Kernel is recompiled once, added possibilities to handle smbfs (reason: forgotten to add reading NTFS disks in the original configuration).

NTFS disks still mounted without any problems.

There is a line in the fstab in /etc directory, which says /dev/hda2 on / type ext2 (rw,errors=remount-ro). By changing this line to /dev/hda2 on / type ext2 (rw,errors=remount-rw) without knowing the reason why the system remounts in read only is like giving aspirin to a man with a broken leg. I think I need to know why this happens before I can take any action.

Is this caused by hardware problems (disk?), a bad kernel or anything else?

Well it is pretty obvious from that fstab entry - upon any errors on the disk, it is to be remounted read-only to avoid any filesystem corruption. Obviously you have errors on that disk and that causes it to be remounted ro. I think that you can safely exclude the bad kernel option, and that you should look into what is going on with the disk.