let access add primary key is greyed out??

[Martin ©¿©¬]

Hi
Using 2007
I am creating a database file from an excel spreadsheet
However, let access add primary key is greyed out
Only choose my own primary key or No primary key is available

Why is that, I have done 13 other tables no bother?

 

[Gwen]

This happened to me when the table I was trying to import had too many fields/columns. The maximum number of fields in Access 2007 and 2010 is 255.