I searched internet and found that this problem can have several
causes

1. You are using the wrong community string

that's not it cause It doesn't give errors on HD and CPU measurments

2. You are not in the acceslist of the box u are polling

Also not it I'm monitoring under an administrator network account with full rights

3. The box is not running snmp

It does or else i could not get other values out of it correctly

4. The box is down

This should mean the half network would be down
considdering it is a terminal server

5. Not the correct hostname

I used the IP adress as the hostname.
GetIf gives information about the device and it definitly is the server I wan't to monitor
Don't know what to do anymore

Any idea's are welcome