using dropbox to trransfer .data folder

I keep getting errors when I try to copy my folder to dropbox. For example, errors occur in csort.MYD, terms.MYD, pdf.index.MYD, jterms.MYD, csortMYD and pdfindex.MYD. There were no errors when I transferred the Endnote database and new style files. Please help me as I am working under a tight deadline to transfer work I have done for someone else. 

According to the knowledgebase article Endnote is not compatible with Dropbox.

Recommended methods for sharing Endnote libraries is to: 1) sync the library to Endnote online and give the recipient authorized access (note that this requires the recipient to have been Endnote online account and you both are running the same version of Endnote, or 2) using Endnote desktop to save the references as a “Compressed Library” which can be emailed to your colleague and contains the .enl library file, and corresponding .DATA folder (containing the PDFs). There’s a 4-gigabyte size limit (on the library to be compressed) and the compressed library file can be restored by the recipient through the Endnote desktop program.