Excel2003 WorkBook with many INDEX/MATCH Formulas ...

Issue ... When I attempt to write a new INDEX/MATCH Formula I am having a
problem with Excel each time I attempt to enter the "M":

=Index(myrange,m ... at this point I receive pop-up stating I have an
"Identify" conflict & I need to select a Cell to use ... Seems no matter what
I do at this point I receive the Error message "Excel has encountered a
problem & needs close".

Above said, my work around has been to copy/paste an INDEX/MATCH formula
from a different cell & then to edit my ranges. But I do not understand why
I am getting error in 1st place or what I should really do.

Sorry I have not identifed the pop-up error message exactly, but I am trying
not to encounter the dreaded Excel shut-down ... Hopefully, I have identified
the error close enough so that those of you intimate with Excel & that
support this board will recognize the symptom.

My many "Thanks" to those of you supplying the many beneficial solutions to
these boards ... Kha