The best place to ask about Excel-DNA is the Google group at http://groups.google.com/group/exceldna.The
latest release for Excel-DNA (version 0.29) is now available on the CodePlex site: http://exceldna.codeplex.com
. It adds support for the 64-bit version of Excel 2010. Support for .Net 4 was added with version 0.27 in August 2010.Some issues you might be running into:* The default target framework version under Visual Studio 2010 is .NET 4. To tell Excel-DNA that it should load the .NET 4 runtime, you need to explicitly add a RuntimeVersion="v4.0" attribute in the .dna file. The error message when you have this problem is pretty descriptive though.* Under Excel 2010 64-bit version you need to use the corresponding ExcelDna64.xll. If you have the wrong bitness for your .xll, Excel will merely complain that the file "is in a different format than specified by the extension."* Under Excel 2010 64-bit version, only .NET 4 is currently supported. * When debugging, you might need to set the framework version for the debugger to match the .NET version your add-in uses.* When trying to debug managed code hosted in a native process from an express edition of Visual Studio, you need to make some changes in the .csproj file.This thread on the Google group gives more details and some links for the last two issues, including the changes you need to make to the project file.If you still have problems after reviewing these issues, you are welcome to post to the Google group of contact me directly.-GovertExcel-DNA - Free and easy .NET for Excel.