I have not yet ported myself to LINQ and .NET 3.5 but:

Eric Carter has recently updated a blogpost on automation add-ins:
http://blogs.msdn.com/eric_carter/archive/2004/12/01/writing-user-defined-functions-for-excel-in-net.aspx

As for the loading process of .NET 3.5 I would test to use an Excel loader, i e a standalone tool to:
1. First to check if 3.5 is running or not. If the later load it.
2. Second load Excel.

By this approach You avoid the excel.exe.config file (which can be easily overwritten unless the enviroment is 100 % controled) and
maybe solve the error generate by the present solution.

In my experience we should be less focused on new tehcnologies when working with older versions of Excel. MSFT focus only on Excel 2007 and the next coming version as they developed with the other new technologies in mind. In other words, I doubt that MSFT will make any patches to solve any bugs between Excle 2003 and .NET.

Kind regards,
Dennis

I am still trying to determine whether it is a bug in my code or something wrong with .NET 3.5 and Excel 2003.

I have a couple of issues. First, when I run the automation add-in (it is a custom formula add-in), the function works. But, part of the feature I have is that on the second call to the formula, it uses LINQ to search an internal cache of objects. It is on this subsequent call that I get a VALUE! error in the cell.

The other problem I have encountered is when I explicitly tell Excel to load the .NET 3.5 runtime by listing it in the excel.exe.config file, I get the generic #NAME! error.

When I run the code in a console client instead of Excel, it works as expected. So, I am trying to determine if it is possible to run a 3.5 runtime in Excel 2003. Am I applying the wrong technology to Excel 2003? I am not sure. It is entirely possible that I have coded some kind of bug. So, I am just trying to eliminate a bug possibility.

My eventual goal is to use WCF from an Excel 2003 client to a Windows service. So, again, I am wondering if this is possible or am I wasting time with these technologies.

Thanks for your quick reply. Any insight you may have would be greatly appreciated.

What kind of issues do you experience?

My standard approach is to code against version 2.0 of .NET Framework. In this way I also get workable solutions in an enviroment where 3.5 is in use.

So far I can conclude that Vista has given me some troubles when I use 2002 or 2003 of Excel.

Kind regards,
Dennis

Yes, You’re right but I thought that any feedback may get lost due to all the pingbacks.

Kind regards,
Dennis