Import process failed due to the error: undefined

Hi. I have the PDF Light Viewer Plugin Pro and im having problems uploading pdf files. When I import PDF (choose pdf file), click the checkbox Enable import and then publish, everything starts ok. Then it goes up to 8% and stops there. I waited for about 1,5 hours to upload 2 page PDF file (pdf size 435kb) but it stays there, 8%. When I checked my medialibrary, there was over a 100 pages of  image/jpeg files of this same (2016/11/pdf-1187-page-00001.jpg) file. I did manage to upload 5 PDF files succesfully before this issue(all of those over 8 pages) but now I cant upload any other files.
Any ideas?
 Thank you,
 -Raitio