ASP.NET web server cannot be launched and Mono environment not be switched

Question

I am running one of the latest versions of Monodevelop on Linux Mint which used to work before I formatted my drive and made a fresh install. When I build my project it builds fine, but when I try to run it I get the following message:

Could not launch ASP.NET web server. The xsp4 web server cannot be found. Please ensure that it is installed.

I have xsp4 and xsp4-base packages installed. I found in a question and answer on askubuntu that I need to switch the Mono runtime to make it able to find xsp4.

When I go to Edit > Preferences > Projects > .NET Runtimes I see the options Mono 3.10.0 (Default) and Mono 3.10.0 (/usr). Unfortunately, when I switch to the /usr one (the one I need and should work) I get the same error as above that the web server cannot be found. And now the weird part: when I look again in the .NET runtimes options I see that is has switched the default back to the original one.

The switching back to another default only happens after I press F5 and try to build the solution (both with release and debug).

Does anyone know how I can fix this?

Answer 1

In case we're running an ASP.NET application on Mono using Monodevelop for the first time, we may receive the below error:

In some cases, the problem is incorrect installation of xsp4 server.

Install it using:

sudo apt-get install mono-xsp4

This solved the above error.

Optional: get it from Ubuntu software center by searching for xsp4

Extra: For Arch (or based like Manjaro...) use yaourt -S xsp.

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