Hello, my name is Dan.
I will do my best to help you, the only stupid question is the unasked one.
That is telling you that the hard drive is full past its ability to function.
A fix is to install your OS X on an external hard drive larger than the internal drive (at least 200GB bigger). Then you can migrate from the full drive to the new, swap drives and it should be fine.
That is the short version, here are some details.
After installing and migrating repair permissions and repair the directories.
Then it should be just fine.
I recommend this utilty for the directories and file repair.
It is not cheap but it is cheaper than losing all your data.
Overall the cost of fixing this will be around $200.00, this includes the new hard drive, the DW software and this question.
This assumes you can swap the drive yourself, it isn't hard and this site will step you through how to do it.
Just indentify your Mac and follow it.
The reason it returns that error is it cannot write to the drive and it has to in order to perform the repais the fsck is trying to do.
Hope that helps.