Could it be that you should be trying to open your current data set not sync to a synced file? Use “Open others” and navigate to your data set folder. Your data set is a folder not a file containing other folders and files. The data set naming convention is yourdatasetname.moneydance.
Unfortunately yr suggestion doesn't apply because I have no .moneydance file: I reinstalled my PC and the old local folder is gone, but I have gone through the same process before with no issues whatsoever, last time in October 2017.
Can you check under FILE – SYNCING and see if the Sync Method is fixed.
You may have recovered what is termed a secondary data set from which you cannot sync any new data sets. However, all the data should be correct. There is a process which can turn a secondary data set into a main data set if you need it. This will allow you to set up new syncing if you need to.
Support have provided a file called "md2017_convert_secondary_to_master.py" that should resolve this problem for you, see attached. Before proceeding, please back up your Moneydance data set, just in case something goes wrong. You can create a manual backup using the FILE -EXPORT BACKUP.
To use the .py file, first save it to your computer, somewhere you can easily access it like your downloads folder or your desktop. Then follow these steps:
1. In Moneydance, select Window --> Python Scripting.
2. In the window that opens, select 'Open Script' then navigate to the .py file wherever you saved it on your system.
3. Select 'Run' to execute the file.
4. Wait a few moments until you see a message on screen, confirming the script has run successfully.
5. Close and reopen Moneydance.
Click FILE - SYNCING, and you should now be able to select the required sync method.