What version of mojoPortal and what version of Event Calendar Pro. I believe this error is a version mismatch. If you are running the latest version of mojoPortal and the latest version of Event Calendar Pro I can try sending you a newer build of Event Calendar Pro as this issue does not happen on my machine nor on demo.mojoportal.com. It is possible that I made a mistake somewhere and need to make a new release of Event Calendar Pro to fix it if this is happening with the latest release. You can see the version under Administration > System Info
You might also try deleting all rows from the mp_TaskQueue table and then try to create the event with recurrences again in case there was a task that was serialized into the db from a previous version.
I don't see a connection with this error and NeatUpload.