If Mapped Network Drive keeps disconnecting on your Windows system, then this post may help you in troubleshooting the issue. Here are a few options being suggested. Check to see what may apply to your version of operating system or scenario.
Mapped Drive gets disconnected
1] Windows will drop idle connections after a specified time-out period, I think it is 15 minutes by default, to prevent wasting resources. You can however, easily re-establish the connection manually. If you wish to turn of the auto-disconnect feature, type the following in an elevated command prompt and hit Enter.
net config server /autodisconnect:-1
2] If it occurs while copying large files over network drives, it could be due to the auto-tuning network introduced in Windows Vista. To turn it off, open an elevated command prompt windows, type the following and hit Enter:
netsh int tcp set global autotuninglevel=disabled
It should help.
3] To turn-off the auto-diconnect feature, you could also edit the Windows Registry. Navigate to the following key in the registry:
Change the hexadecimal value of autodisconnect to ffffffff. Click OK and Exit.
Alternativey, you could also download and apply this Fix It from KB297684.
Hope something here helps you resolve the issue.