SYNC ERROR: We have been unable to establish a connection with QuickBooks. Please try again. These instructions show what to do when you get the following error. SYNC ERROR: We have been unable to establish a connection with QuickBooks. Please try again. STEP 1: Open the Sync Manager and click on Setup. STEP2: Make sure you are in Single User Mode and that your QuickBooks Desktop is open. Click Next. STEP 3: Enter your InvoiceASAP username & password. Click Connect. STEP 4a: If you are normally in Multiuser Mode, change back to Multiuser Mode now. If you want Auto Sync, make sure the settings are what you want, and click Done. STEP 4b: If you don't want Auto Sync, then please uncheck the Run Auto Sync checkbox, then click Done. STEP 5: The sync starts running. STEP 6: A successful sync displays the happy face! Have more questions? Submit a request 0 Comments Please sign in to leave a comment.