When trying to bring up the Method Sync Engine, you may get this error:
"QuickBooks already has a company file open. If you want to open another company file, close this one first. Only QuickBooks Accountant and QuickBooks Enterprise Solutions can open two files at once."
In order to fix this issue, please follow the following steps.
Get the location of the QuickBooks file. Find the location of where the QuickBooks file is stored by pressing the F2 button while you are in QuickBooks.
Navigate to the folder that holds the QuickBooks file.
Close the QuickBooks file and Method Sync Engine.
Open the QuickBooks file from the location rather than from running the program itself.
After the file is open, connect the Method Sync Engine again and it should work.
You can also try restarting the computer if the above solution doesn't work.