I too received this error for one client transferring from 2017 to 2018.  A Lacerte rep interacted with my computer,  looked through all the 2017 data details of the one client using CTRL W.  He spotted a "weird" description in the itemized medical data.  "We" deleted the input and the client proforma to 2018 "like butter."  Only took about 45 minutes to resolve.  He told me that "usually" it is a Charitable Contribution input issue.