This is a (sometimes) bug, at least in Discoverer 3.1 and I see it on some machines when I first install Discoverer. One or two queries may work, and then your message (with garbage characters for the "file name") from then on.
The program seems to fail to correctly set the cache sizes in the registry (or ini file or whatever it's saving stuff) from the Preferences.
What fixes it for us (every time) is:
1. Pull down the [Tools] menu.
2. Select [Options].
3. (Scroll right if needed to) select the [Cache] tab.
4. Set the [Memory Cache] and [Disk Cache] values. You can set them to the values they were going to default to anyway, just type in there and then put it back to the original value so it sees they were "modified" and saves the values when you...
5. click [OK]
Apparently the installation defaults are not reliably saved in the first place. "Changing" them in the [Options] dialog will, however, reliably set them and that always cures this problem for our users.