I am programmatically naming cells based on a header row and their
position. The problem is not in code but in a name I am trying to use.

I am trying to name a cell 'C2a.1' and I get 'That Name is not Valid'.

When doing this manually I get the same error. Looking at the help I
know I can't name a cell or range like a valid Excel reference e.g. A2
or $A$2 or R1C2 etc... but this is a mystery to me!

Any ideas?

Steve