Navigate the the location below in your registry and make the corresponding change.

Create or edit the existing DWORD value (string value for Windows 98) named "PMTUBlackHoleDetect" and set it to either "1" to enable detection or "0" to disable it. 

Restart Windows. 

Key:[HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\VxD\MSTCP]
Value Name: PMTUBlackHoleDetect
Data Type: REG_DWORD
Data:(0 = disabled, 1 = enabled)