We had an ASP.NET site that was built on .NET 2.0. It had sharepoint integration and everything was working fine until the site got migrated to .NET 4.0. I know that sharepoint is built on 3.5 framework and hence it is failing now. Are there any workarounds or any latest developments to make sharepoint work on ASP.NET 4.0 site?
You have probably read .NET Framework support in SharePoint 2010 ?
Basically, it stated that SharePoint can't run on .Net V4 (I guess it's because of the workflow engine, but it's only a supposition).
If you require something that works with V4, you have to create your own application. This application can then consume data in SharePOint using remote api (Client object model or web services).
Or you can wonder what in the .Net V4 that does not exists in the V3.5 is actually required, or can't be rewritten.