How to resolve F5 VPN Connection issue

As before, I have to do some homework at home in holiday so that I need to connect to the corporative environment by VPN. When I connect to VPN Server by IE and pass the authentication next to click “Access Network Resources” hyper-link, its error status is “Network Access Connection Device was not found”
In the moment, I still follow my troubleshooting rule --- Based on the error message to search the information by Google. Although I get some information to try and error as uninstall F5 VPN driver next to reinstall it again, the result still fail again and again.
Until I find out that VPN function is the relation with Remote Access Connection Manager Service by System Event Viewer.
So I decide to search the information based on this word. Finally, I get the answer to workaround this problem. That is Edit Registry Key Value!
In Registry Editor, Select “\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services\RasMan” –> Right-Click “DependOnService” –> Click “Modify…”
The Value Data will exist two strings --- Tapisrv and SstpSvc
Please delete “SstpSvc” next to reboot the computer.
Now you can connect to VPN Server and Remote Access Connection Manager Service will be started.
Although the above problem can be resolved, I still don’t know Why?
Maybe need to research F5 VPN theory if I can touch F5 device in the future.