Mailbag: Do I need still need older versions of the .NET Framework on my system after installing the .NET Framework 4?

Note: This is an updated version of a previous mailbag entry that I posted before the .NET Framework 4 shipped.

Question:

I recently installed the .NET Framework 4 on my system. Afterwards, I looked in Add/Remove Programs, and it shows that I have all of the following versions of the .NET Framework installed on my system:

  • Microsoft .NET Framework 1.1
  • Microsoft .NET Framework 2.0 SP2
  • Microsoft .NET Framework 3.0 SP2
  • Microsoft .NET Framework 3.5 SP1
  • Microsoft .NET Framework 4 Client Profile
  • Microsoft .NET Framework 4 Extended

Do I need any of these older versions of the .NET Framework now that I’ve installed the .NET Framework 4, or can I safely uninstall them?

Answer:

In general, my recommendation is to leave the .NET Framework 2.0 SP2, 3.0 SP2, 3.5 SP1 and 4 installed on your computer.

Unlike previous versions of the .NET Framework, the .NET Framework 4 does not allow an application that was built with previous versions of the .NET Framework to migrate forward and run on it if the previous version is not installed. If you are using any applications that were built with any version of the .NET Framework before version 4, then I recommend leaving both the .NET Framework 3.5 SP1 and the .NET Framework 4 installed.

You cannot use the .NET Framework 3.5 SP1 unless you also have the .NET Framework 2.0 SP2 and 3.0 SP2 installed. Therefore, you will not be allowed to uninstall the .NET Framework 2.0 SP2 or 3.0 SP2 if you have the .NET Framework 3.5 SP1 installed. If you try to uninstall the .NET Framework 2.0 or 3.0 when the .NET Framework 3.5 is installed, their uninstall processes will block and tell you that they are needed by another application on your system.

The .NET Framework 1.0 and .NET Framework 1.1 can be installed side-by-side with the .NET Framework 2.0, 3.0, 3.5 and 4. Most applications that were created for the .NET Framework 1.0 or 1.1 will automatically use the .NET Framework 2.0 instead if it is installed on the system. In most cases, that means you do not need to keep the .NET Framework 1.0 or 1.1 installed on your system if you already have the .NET Framework 2.0 installed.

However, there are some applications that are configured to require a specific version of the .NET Framework, even if later versions of the .NET Framework are installed. If you have any applications like that on your system and try to run them without installing the .NET Framework 1.0 or 1.1, you will get an error message that looks like the following:

---------------------------
MyApplication.exe - .NET Framework Initialization Error
---------------------------
To run this application, you first must install one of the following versions of the .NET Framework:
v1.1.4322
Contact your application publisher for instructions about obtaining the appropriate version of the .NET Framework.
---------------------------
OK
---------------------------

In the above error message, the version number will be v1.0.3705 if you need to install the .NET Framework 1.0, and it will be v1.1.4322 if you need to install the .NET Framework 1.1.

If you end up seeing any error messages like this, you can re-install the .NET Framework 1.0 or 1.1 in order to resolve the errors. If you don't end up seeing any error messages like this, then you don't need to worry about re-installing the .NET Framework 1.0 or 1.1.