If you are working with VS 2010 (any Edition) and cannot open your 2010 solution on VS 2008 then just follow these 3 Steps:

For .sln:

1. Open the solution file in your favorite text editor (ex: notepad++).

2. Find the Following:Microsoft Visual Studio Solution File, Format Version 11.00.# Visual Studio 2010.

Replace with: Microsoft Visual Studio Solution File, Format Version 10.00. (I)# Visual Studio 2008. (II, optinal)

For .csproj/vbproj:

1. Open project file in your favorite text editor (ex: notepad++).

2. Find the Following:.

Replace with: .

(III) Thats it..Now you can open your solution file on VS2008.Reverse of this will enable VS2008 solution to open in VS2010.