Archive for June 2011

Unable to determine the URL to the Xap file from web

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I encountered today this undocumented error: “Unable to determine the URL to the Xap file from web XXX”, after renaming one of my silverlight 4 projects, which was set to run Out of Browser.
Supposing you renamed your project from XXX to YYY.
To fix the error above, go to your YYY.csproj.user on the disk, and open it for editing with notepad.
Then change


Now save it, and you’re good to go.

Usually *.csproj.user files should not be under source control.
So if you rename a silverlight project which a colleague of yours has set it to be ran out of browser on his computer, then he will get this error unless you share the same *.csproj.user on the source control (which is not a good idea).

I think a visual studio 2010 improvement is needed here, that describes the situation better. Something like: “Unable to determine the URL to the Xap file from web XXX. If the project was renamed, please rename it inside your *.csproj.user” file settings as well”


Written by Liviu Trifoi

June 1, 2011 at 8:48 am