DLL that takes and returns ranges does not always work

Hi,

I have a DLL written in C++ that takes ranges as arguments and returns also
a range. For some reason it does not always return numerical values. In
other words, I need to click "Shift+Ctrl+Enter" repeatedly to get it to work.
When it does not return numerical values, it fills in the cells with
"#VALUE!". Any idea on how to fix this?

The DLL has an embedded optimization process that runs longer for certain
input values. Could this be a problem? Do I need to slow Excel down somehow
to make it wait for the DLL to finish the optimization. If so, any idea on
how to do this?

Thanks tons!

PS: Here is my linker line in Excel:
Declare Function baBDTTree Lib "C:\...\BDTdll.dll" (a() As Double, b() As
Double, c() As Double, n As Integer, deltaT As Double) As Double