"do you want to know troubleshoot multi user issues in QuickBooks for mac. Fixing multi-user issues in QuickBooks for Mac
Verify that your QuickBooks server is running and the company file is shared or not.

Firstly you click on Go from an Application.
Double click on the QuickBooks server.app icon which is used by you(like 2010,2011 and so on).
Share that file if you needed:
If your file is listed under Not Shared, select that file or click on Start Sharing button.
If your file is not listed, click on “+” button in the lower left corner to add your file."