I recently upgraded an ActiveX EXE built in VB6 that is used by a few Excel
spreadsheets. I preserved binary compatibility when I compiled the project.

I can use the ActiveX EXE without any problems (it queries our database)
except in some cases where an existing spreadsheet that has a reference to it
set when the old version of the EXE was around. We found one old XLS that
didn't have a problem with the new EXE (which it shouldn't since the binary
compatibility was preserved). But others give the error 430, which seems to
go away if I drop the reference to the EXE, close and save the XLS, then
re-open it an restore the reference.

Is this a bug in Excel (version 2003)? Why would any XLS which is using a
binary compatible ActiveX EXE complain but others would not? Is Excel
caching something it shouldn't?