paypal will not allow removal of a funding source if there is account activity.
Does not matter if there are other sources on the account, paypal send that message.
I get that on every account if I attempt to remove a means of paypal being paid.
even get an email that scares me
As far as I know it's not a glitch. Been happening for months 
__________________ REAP WHAT YOU SOW. LIFE IS SO NOT FAIR. | 
