I've installed the software, connected to 3 projects, and successfully processed the data for those projects...and now all of the data I have (18 tasks) is marked as "Uploading" in the task tab. In the Transfers tab I can see that they try to upload, quit, and schedule themselves to try again later.

It looks like they always upload the same amount of stuff (871 bytes?), and then fail, as the size column tends to have entries like:

0.84/39.43 KB
0.84/159.80 KB
871/10 bytes
0.84/22.67 KB

etc.

I'm not getting any visible error, and nothing is showing up in the vent log. I'm guessing it may be something weird like our firewall trying to append something to the upload? Is there some way I can troubleshoot this?

I don't know what a vent log is, but when BOINC uploads fail, messages about it are shown in the Messages tab of the BOINC manager.

As the files are very small, it's possible that they're being blocked by a firewall.
In which case, look in the menu of the firewall software for an option to allow BOINC through it, or to give BOINC "trusted" status.

"event" + bad typing = "vent".

Messages: ahh...one would have thought I could have looked there. Thanks.