I have had this issue and it is one of the following or even the "perfect storm" of both of them.
QuickBooks was installed incorrectly and needs to be uninstalled and reinstalled not as a host.
I have also found the network mapping to the database to be an issue in some cases. Verify the path and be sure it has been set up correctly. In fact I always redo it from scratch.... carefully.
Not a bad idea to do both of these to fix the issue.
