What is the best setting to create SWF file that is uploaded to Wix?
You should create and compile your SWF file using Action Script 3. If you received an error message, it is because your file was compiled using Action Script 2.
The frame rate in Flash files is set by the loading application, (in this case the wixviewer which runs 25 frames per second). Make sure that you create SWF file at 25 frames per second (that way it'll work the same on your local machine and on Wix).
Users who wish to upload complex SWFs containing code should upload them to a separate document first. This document can be used as a testing ground for media items and deleted if corrupted.