QuickBooks network connection error pops up when the application can’t access the company file. This could result from a severed connection with the system hosting the company file or to different settings blocking this access. Moreover, antivirus and power optimization can also disrupt the connection. 

• To fix the QuickBooks connections has been lost error, try restarting your system and database server manager. 

• Further, change the sleep optimization settings to never and change the location of the company file. 

• Run Quick Fix My Program and QuickBooks File Doctor if the error persists. 

• Moreover, fix the hosting issues in other systems in the network. 

• Another thing you can do is to remove and recreate .ND File.