Still no working

I did the try, same error message.
HTTP 500 - Internal server error
or The requested resource is in use.
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1. If I use "1.html" which is non-existing,
it will show "The page cannot be found"
2. If I use "1.asp" which is non-existing either,
it will show "The requested resource is in use"
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3. If I use "2.html" which is real existing,
it will show up.
4. If I use "2.asp" which is real existing,
it will show "The requested resource is in use"
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It really can't figure up what's going on here,
any other suggestion ?
Thank.