Can't delete field

Hi,
I can't delete a Formula field on one of my forms. I get the error message..

Data in this form is being processedfor Formula calculation. You cannot add/modify/delete fields in this form till the process is completed. Please wait till it gets over.

My application is called Elections and the field is called Hub Contacts Reference on the Hubs tab.

Can you have a look at this please?

Thanks,

Lee