There isn’t much out there on this error. Before doing any data update, I like to export the target object’s full data set as a precaution. My tool of choice is workbench but sometimes it can be a little baby and complain like “Selecting compound data not supported in Bulk Query”.
Turns out that the following fields are going to make your bulk api export fail:
Address fields like:
Latitude and Longitude fields like:
These are your most common “compound” fields. Once you remove these fields from your export, you should be ok.