Forms Created in Pro 10 cannot be signed in Reader 11

Hello,

I have created forms using Adobe Pro 10 with signature fields.  Users who recently were upgraded to Reader 11 can no longer sign the form.  They can enter data into text fields - but when reviewing the form properties it disallows digital signatures.  If I open the form back up in Pro 10 edit mode - i see that all properties are enabled - to include signatures.  I cannot figure out how to modify the forms to allow Reader 11 access to sign.