Q: transfer photos library to new mac: error code

I'm trying to transfer my photo library from an el captain 2012 macbook to my new late 2015 iMac.   Its about 65gb and almost gets done transferring to an external drive (so I can move it over to the new iMac) and it throws a "finder can't complete..... some data can't be read or written. error code -36".   I did export all photos so I have them, but then the exif data is not complete (i.e the date specifically is agitating its not included in the export).  So back to the drawing board of trying to transfer the actual library.  I then followed the instructions to rebuild the library, and tried transferring to the external hard drive again... same error code.  I don't use the photo app for anything other than storage of my bazillion iPhone photos, so I'm not even sure what would get hung up.   Any other advice is appreciated!

Note:  my old 2012 iPhoto archived library transferred fine.