This value must be unique (ID)

I have a form that visitors fill in.

If more than 1 person fills in the form at the same time, the other users get the message

'There was a problem with your submission. Errors are marked below.

abstract_id

This value must be unique."

Is there a way that the form can be submitted by multiple people. The ID field in question is of the form

"17-123"

it is "single line text", unique, read only. it takes its value as a "dynamic value" as "17-[dcrxra]"   where [dcrxra] is an auto_increment field with value "[auto_id start=1]"

I do this as the ID field needs to be reset each year, so this year it starts at 17-001 and auto increments up.

Next year it starts at 18-001

The abstract_id field needs to be able to be edited at later date.

Any ideas? (apart from making the abstract_id NOT unique?)