Run-time error 2176

Hi,
I am populating a combo box with rowsourcetype "Value List" with a record set of invoice numbers.
While this has worked ok for some time, this form has started generating the error "Run-time error 2076 The setting for this property is too long".
I think it's something to do with how many records I'm trying to put in the list (10 characters but >2000 records).

Please advise.

Thanks
Paul