The vendor table in the database is probably be locked by another program or source such as a report. Run another sync after closing anything that may be using vendors.
It may be that the error below may appear in your QuickBooks sync during the vendor portion. Basically, this error is just SQL Server saying that it took too long to try to access vendor information from the database and it gave up on doing so.
Error Vendor [SynchronizeQBVendors]Microsoft OLE DB Provider for SQL Server (-2147217871) Query timeout expired
Usually, this is because the database table that Acctivate uses to store vendor information is being locked by another source. For some users, this was found to be a third party program that was accessing that part of the database during the sync. However, it's also theoretically possible that Acctivate's reports could do the same thing since they are generated by the program Crystal Reports.
If you're receiving this error, try closing any reports that could access vendor information and, if applicable, any programs that could be doing the same thing. After that, try the sync again. If the problem persists, submit a ticket to the support team for assistance.