Windows Phone 7 WiFi Connection Unsuccessful
Windows Phone HTC 7Pro tried to access internet through my WiFi when I tried on my WP7phone the “Connection unsuccessful” contact your network administrator error, I spent four days to figured out the solutions.
Initially I doubt on Windows Phone device may be missing some of the fixes, I have done the all the update and tried to connect to WIFI again the same issue, then I started looking at my WiFi Device.
I got suspect on my WiFI device may be the this device firmware old or configuration issues.
before updating the firmware on my device, I have checked the Authentication Settings
I was set as below Figure.

Authentication Set to “ WAP2-PSK”
I have checked to new setting as below

I have changed to “WAP-Auto-PSK” now I am able to connect to my WiFi from windows Phone 7.5mango.
if you face similar issue, first try to update your WiFi device Firmware then then check the configurations.