I am certain you will need to have either the dot net 2.0 framework installed or there will be 2.0 assemblies that will need to exist at the installation level. There are different dll's in dot net 2.0 and 4.0 that do the same thing but rely on that framework level assemblies. If you have this application working on a machine that only has dot net 4.0 installed, then it must have been setup to copy the specific assemblies that were needed.

>Hi Tim,
>
>Thanks for the reply. Your comments are exactly what I am trying to determine. I.e. is the dll's specific compile framework required, or are runtime frameworks backward compatible?
>
>The reason I am asking is we have a client ( remote so we can't determine machine config ourselves ) that seems to have placed a .Net 2.0 exe on a machine that (supposedly) only has the .Net 4.0 Framework on it and the application seems to run. We are trying to get further details of the exact machine config.
>
>Bill
>
>>>We haven't run into this issue before and are trying to get some quick answers w/o doing research.
>>>
>>>1) Will a .Net application developed/compiled under an earlier .Net framework ( e.g. 2.0 ) run under a later framework ( e.g. 4.0 )? I.e. will an application compiled under .Net 2.0 is placed on a machine having only .Net 4.0 run properly ( or at all )?
>>>
>>>2) If a machine has more than one .Net Version Framework installed on it, will each appliction/dll on the machine run under it's compiled framework, or will the OS run all applications/dlls under the latest framework on the machine?
>>>
>>>Thanks,
>>>Bill
>>
>>Many of the dll's are different from version 2.0 to 4.0. If the application is using the dll's from dot net 2.0/ 3.0/3.5 you will need to have that framework installed as well.
>>Tim