.NET Framework v.4.0 doesn't load url with index.php?url=

So I've been using .net framework v.2.0 with IIS 7 for my website then recently it kinda start to load really slow and at the bottom left of the website it shows waiting for available socket....

I tried changing Application Pools DefaultAppPool framework from v2.0 to v4.0 and it loads the website normally but then I realized v4.0 doesn't let my website link such as index.php?url= to work it just redirect back to my website homepage.