You should stop the MSSQL ACT! service temporarily to be able to sync files:

1) In Windows, select Start -> Control Panel -> Administrative Tools -> Services.

2) Locate the service named "MSSQL$ACT7" (or something similar).

3) Right click the service name and "STOP" the service.

4) Now open GoodSync and click Browse on the left side and select ACT! folder.

5) Click Browse on the right side, selecting where you would like to back up or sync your data to.

*Note: by default you are performing a sync, if you want to back up instead, first select Job > Options > 1- Way Left to Right, and then continue with step 5)

6) Start the sync/backup process by clicking the Analyze button.

7) Click the Sync button to complete your sync/backup.

*Note: You can now go back to the service, right click the ACT! service name and choose START to restart the service.