[WD22] Webservice "500 internal server error"

Hi,

I have created a webservice via *.awp sites at a Windows 2012R2 server (Hyper-V).
After a long time of inactivity (~30 min) the first http-request ends with "500: internal server error".
The second try works like expected- It looks like the server sleeps and need a wakeup :-)

Any Ideas why and how to repair this behavior ?