File system becomes read only spontaneously

[bullginger]

Something that has been happening rather frequently lately is that the xbian filesystem will become read only spontaneously. This has been happening every couple weeks and each time I just reinstall, upgrade, and restore from backup. I have not been able to figure out what is causing damage to the file system. It will happen at time when it is running but not in use. I'll simpliy ssh into it and see and error saying the filesystem is read only.

I am using a model b raspberry pi. Could this be a power supply problem? I am using an iphone charger as a power supply which provides 1 amp which should be enough. Could the cable be causing an issue?

I turned off overclocking just in case that was causing the issue but the file system will still become corrupted.

Could it be a bad SD card? Is there a way to check it?

I have a usb hard drive attached but with external power, incase that information helps.

Any help is appreciated.

Thanks