Problem when adding a jpg / jpeg / pdf archive to a blank diagram

[lloviendo]

Hello, i´ve purchased recently the Neck Diagrams software, and I've working with it a few months without any problem.
But two days ago i can't add any jpeg, jpg or pdf image to any blank diagram... sometimes I repeat the process and it works but i have to spend a lot of time in it and I cant understand why happens this incidence...
I've tried to convert the file to other image formats but it's always the same.
I use Mac OSX Snow Leopard 10.6.8. and Neck Diagrams v. 1.11.3
Thank you for your attention and excuse me for my poor english... i hope you can solve this problem because i love this program and i cant work without adding any image files to a blank diagram…