What happen if you don't specify this in the configuration file ?
I mean that purpose that is serve?
<configuration>
<startup>
<supportedRunTime version="v1.1.4322 />
</startup>
</configuration>
http://msdn.microsoft.com/en-us/library/w4atty68.aspx
says
<quote>
If the <supportedRuntime> element is not present in the application
configuration file, the version of the runtime used to build the
application is used.
</quote>
There are also:
http://msdn.microsoft.com/en-us/library/w671swch.aspx
<quote>
The runtime examines the <supportedRuntime> Element element in the
application configuration file. If one or more of the supported runtime
versions specified in the <supportedRuntime> element are present, the
runtime loads the runtime version specified by the first
<supportedRuntime> element. If this version is not available, the
runtime examines the next <supportedRuntime> element and attempts to
load the runtime version specified. If this runtime version is not
available, subsequent <supportedRuntime> elements are examined. If none
of the supported runtime versions are available, the runtime fails to
load a runtime version and displays a message to the user (see step 3).
The runtime reads the PE file header of the application's executable
file. If the runtime version specified by the PE file header is
available, the runtime loads that version. If the runtime version
specified is not available, the runtime searches for a runtime version
determined by Microsoft to be compatible with the runtime version in the
PE header. If that version is not found, the process continues to step 3.
The runtime displays a message stating that the runtime version
supported by the application is unavailable. The runtime is not loaded.
</quote>
Regarding what is compatible then there are at least an example at:
http://msdn.microsoft.com/en-us/library/ms994381.aspx
see the "Application Load Mechanisms and Possible Issues" table.
I can not find a similar page for 2.0 versus 4.0, but I will
expect it to be the same that 2.0 stuff will run on 4.0 if
necessary.
Arne