Because the location you are openining the project is not trusted by your runtime, however, I have never seen this with a web application but see it very frequently with Windows applications. In any case, as long as you trust the location you are opening the project from you should be ok.
VS is telling you this because it could potentially cause the code to be executed with full trust permissions which can be a bad thing.
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Read this if you want to know how to get a correct reply for your question:
http://www.catb.org/~esr/faqs/smart-questions.html
^^Took that from planoie's profile^^
^^Modified text taken from gbianchi profile^^
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Technical Editor for:
Professional Search Engine Optimization with ASP.NET
http://www.wiley.com/WileyCDA/WileyT...470131470.html
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Why can't Programmers, program??
http://www.codinghorror.com/blog/archives/000781.html
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