For the site in question, I'm running 3.0.1.
I deleted Ultimate Tag Cloud after the problem and went with Random Tags Cloud instead.
Just now I went back and installed Ultimate Tag Cloud again, getting version 1.1 - I didn't get the error code any more, but I also didn't get the functionality I needed.
The feature I was most interested in with your plugin is the exclude feature - it works for me fine on the Random Tags Cloud widget (simple comma separation of a list of the tag ids I don't want to appear) but it didn't work on the Ultimate Tag Cloud - it allowed me to enter them and save it, but the tags I wanted to exclude kept appearing anyway, even though I tried adding or removing spaces.
One other feature I'd be VERY interested in finding, though none of the plugins I've seen so far can do it, is the ability to create a tag cloud that can be sorted by Tag slug or even ID rather than the name. I'm using tags to list faculty names at my school and would like to sort by last name but have the link appear with the full name.
If I could find a tag cloud that lets me exclude some tags (I don't want faculty who have left to show in the cloud) and sort by tag slug, I'd be very happy!