SCENARIO
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Customer migrates his asp.net 1.1 app to asp.net 2.0 app using VS2005 and WAP. He then started working on it. A month ago he created a backup of the application by copying the entire content folder onto a different drive. D:\Backup\appname.One not so fine day he decides to rollback the changes to his current project C:\inetpub\wwwroot\appname so he copied all the files in D:\Backup\appname to C:\inetpub\wwwroot\appname.

Now when he opens the project in VS2005, it opens as a website instead of a WAP project which is undesirable as the views are different.

I found that the .webinfo file was causing the issue. Deleting the .webinfo file resolved the issue. Now the WAP project opens as a WAP project. I am unsure why or how the webinfo file creaped into the project folder because creating a new WAP project does not include the webinfo file.

See a similar issue documented in  You cannot open ASP.NET Web application project after deployment
http://support.microsoft.com/kb/830611/en-us?spid=3041&sid=147