How exactly are you attaching to your DLL file? It sounds as if you are
losing the link so it would be good to know how you are attaching in the
first place.

"Another frustrated developer" wrote:

I have implemented a wonderful RTD Server in c# that works like a dream.

However, After you open Excel, enter the RTD formula (You then get the
MSCoree.dll contains macros prompt - to which you answer yes) and get a
result. If you then close the workbook, so that Excel has no book open, and
then start a new workbook and type the same formula in you just get #N/A ???

I cannot for the life of me work out why. The only way to get the RTD
formulae working again is to close Excel and open it again.

Any Ideas anyone??