% in URl not working

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C#

ASP.NET

Hello Every one,
I was struck with a different situation in my project. I have a search box to search products in the store. they can search with specail characters also ... I am just sending the search text as a query string to my Search page
So I am encoding the special character to avoid 400 Bad request which takes as a illegal path characters . So i am ok with encoding.... but my main problem is that when I tried to search like

Search Keyword : Product33%

Encoded : Product33[%25]

Results : Search executed well and prodcuts listed out at first search attempt

Url Path : "....Search/Product33[%25]"

without refreshing the page i gave another search word

Search Keyword : PenDrives

Encoded : PenDrives

Results : HTTP Error 400. The request URL is invalid.

Url Path : "....Search/[%]"

first search is working fine with "%" and when i tried to search on another search key the page is error ed out .... Remaing all cases are working fine except if we tried to search with %

Thanks in advance...