I know that sending the request in GET method will solve this problem

No, I don't think so. It has been awhile since I accessed an MS ASP.NET website, but basically when you get the web page, it will contain a "viewstate". This is a very long string that represents what you are doing on the website, like what page you are looking at now, who are, etc. You need to use POST, not GET. When you send your POST, you need to "barf back" verbatim the latest "viewstate" that you received. When you get a reply page, you will get a new "viewstate" string. When you send the next request, you need to post this latest "viewstate".

The basic idea of a "viewstate" is that the client keeps track of what is going on instead of the server. You as the client are acting as distributed storage for the server. For you, this string is absolutely meaningless. Just get it, save it and use it for the next request.

Update:

I just looked at a typical "viewstate". It is 182 lines (formatted like below, of course there are no line breaks in this string) of gibberish. You don't have to decode this, but you do have to barf it back to the server when you send a request. And you will get a new viewstate in the resulting page. 

viewstate is:
"/wEPDwUKMTM0NjAxNTIwMA9kFgQCAQ9kFhACAQ8PFgIeBFRleHRlZGQCAw8PFgQfAAUHU
+2l
nbiBJbh4LTmF2aWdhdGVVcmwFPC9Mb2dpbi5hc3B4P1JFRkVSUkVSPS9teVVTR0JDL01lb
+WJ
lcnMvTWVtYmVyc0RpcmVjdG9yeS5hc3B4P2RkAgUPFgIfAAWUIDx1bCBjbGFzcz0nbmF2J
+yB
pZD0nbmF2MSc+PGxpPjxhIGNsYXNzPSdtZW51X3RpdGxlJyBpZD0nbGVlZF9idG4nIGhyZ
+WY
9Jy9MRUVEJz5MRUVEPC9hPjx1bCBjbGFzcz0nc21lbnUnPjxsaT48YSBocmVmPSdodHRwO
+i8
vd3d3LnVzZ2JjLm9yZy9EaXNwbGF5UGFnZS5hc3B4P0NNU1BhZ2VJRD0xOTg4Jz5JbnRyb
+zw
vYT48L2xpPjxsaT48YSBocmVmPSdodHRwOi8vd3d3LnVzZ2JjLm9yZy9EaXNwbGF5UGFnZ
+S5
... total of 182 lines like this ....
"

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In reply to Re: Validation of viewstate MAC failed by Marshall
in thread Validation of viewstate MAC failed by Anonymous Monk

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