On what platform do you get this problem?
I remember I had the same on a Linux machine with Oracle 8.0.4
First of all look for free resources on the machine you are working on.
Second look if your /var/tmp is full.
I had to reinstall the entire product.Then it worked fine with all the OS user but it is the last thing to do because if the problem depends on the machine you're using may be it could be come back later.
I had it only 1 time and only on Linux platform but i think it does not depend by the OS.