Unable to create equipment with external number A001

Hi Experts,

I am unable to create equipment with external number A001, getting an error "

Equipment number A001 not in external number interval

Message No. IS042''

However it is allowing me to create equipment starting with other alphabets i.e. B001, C001 etc..

I have maintained the external number Range AAAAAAAAAAAAAAAAAA - ZZZZZZZZZZZZZZZZZZ..

Let me know if I am missing anything..