As I was finished entering my info, turbo tax came to charitable contributions and said line 12b had an unacceptable amount in it. No idea why. I entered everything right

Please return to the Deductions & Credits section, scroll down to "Charitable Donations" and DELETE any cash entries you made there. 

Go back through the review. The program will ask you for that number again although it may not be until the END of the FINAL REVIEW. 

Enter the amount up to 600 Married Filing Joint.  

Kludgy workaround.

Intuit needs to get off their collective 4th points of contact and FIX this properly.

Your KLUDGE will not work for ME.  I want to choose Itemized Deductions so that the donations in excess of $600 will carry over to next year when my income will be significantly higher.....