Sync problems - mix of versions and of computers

I have sync issues. I have been using DT from DT2 and onwards. Some of my databases are created in DT2, some in DT3. However, none of my databases syncs to my 2dn computer. What could be the problem?

I sync using Dropbox. My sync store is named with my email, which means a ‘.’ and a ‘@’ is included. I understand that might cause errors. Should I set up another sync store (if yes, how do I delete the old one? Would that be ncluding the files?)

Through times I have had DT installed at several computers - could that be the reason that the sync does not work?

Thanks in advance!