also what OS/Moodle version are you running?
I'm having the same problem here, and the unicode setting didn't fix it.
Moodle 1.5.3, PHP 5.0.4 (can't get 5.1.1 to work), Apache 2.0.54.
The Excel spreadsheet that opens has, what looks to be, the drop-down list for the sub-groups, then a lot of gibberish.
Thanks for helping us think this through... Derry
I have come to the conclusion that the problem has something to do with either "separate groups" or setting a limit on the number of times a choice can be chosen. I tried another choice without these restrictions and the download works fine. Quizzes also work fine.
We are using 1.5.3+ and PhP 5.0.2. I believe when my initial problem was posted, we were using the previous stable version. We use a Windows 2000 server.