Custom fields - Currency Problem

Hi,

I just created a currency field which should hold a value in GBP. I published all the changes and when I try to enter the value into the field, this error comes up:

"A Currency is required if a value exists in a money field. Select a currency and try again"

What am I doing wrong? I believe that currency field has not been created correctly, but I don't know what to change.

I would appreciate any advice.

Thanks

Monika