Intuit has issued an 'Important Alert' reporting that "due to higher than normal activity with Sync Manager applications and e-filing 1099s, some users are unable to sync and are receiving Server Busy errors." Intuit says that they "are working to increase server capacity at this time."
The following information comes from their Knowledge Based Article (KBN) # SLN90117:
Sync Manager error: Server Busy when e-filing 1099s in QuickBooks (unable to sync)
When attempting to setup the Sync Manager in QuickBooks to e-file your 1099s, you may see an error...
Server busy: Sync temporarily delayed. Go to the Sync Manager Application and click on Sync Now button to sync immediately.
If you experience this problem, Intuit's recommendation is that you:
"Try to sync again later, and if you are still unable to, try performing the sync after 5pm PST."
For more information, or to sign-up when the related KBA is updated with additional details, see the KBA at this webiste.