While exporting the expense report to QB Enterprise, you may get an error message like below
QB enterprise has multi-user mode and single-user mode. However, the user has to make sure he is logging in as single-user mode and once the user is logged in as single-user mode in QB then try the integration.
Also, please find the below link which will provide you with additional information if the above solution did not work.
Fix QuickBooks Already Has a Company File Open Error (9 Steps )