QuickBooks Error 6073 99001 can arise in a number of situations, the most common of them being, when the company file is being accessed on the Host computer, and in the single-user mode. You can rectify the same following the steps below -
Close all applications and open QuickBooks on the Host device.
Click on the File button and tap on the Close Company option.
Here, you must close the file and open it again.
Tap on the File tab again and select the Open or Restore Company option
Press the Open a Company File option and hit the OK button.
If this is not the case with your software, you must speak with the experts available at TFN in order to resolve QuickBooks Error 6073 99001.