I have a server that is running all versions of .NET Framework, from 2.0 up to 4.0. An application I need to deploy won't run correctly on later versions, and was originally compiled for 1.1. Is it safe to install version 1.1 on the machine without causing any problems with the later versions?
Edited to add:
To the accepted answer I must comment on how it went after actually installing .NET 1.1. It went fine, except there was one problem that occurred. Sql Server 2005 Developer Edition was on the machine, and after 1.1 was installed, Sql Server Management Studio was no longer working correctly, and had to be removed and re-installed. Only a small problem, but noteworthy.
Yes, you're good to go. .NET framework versions are designed to install side-by-side. The other versions of the framework will happily continue on with their lives.
One thing I will add is that sometimes newer versions of the framework will patch older versions if necessary.
http://msdn.microsoft.com/en-us/library/bb822049.aspx
.NET 4.0 is also a new, isolated version that can run beside any of the others without interferience.