problem with copy and past between two different sequence

Hi everyone.

When I copy a clip, or part of a clip, from a sequence and then I paste the copy clip into another sequence and try to move it, Premiere completely stop working until I forced exit.

The crash happens almost every time I make a past a copy between different sequences.

in the exact moment when I force the exit, the clip seems to be in the correct position but then the software crashes, warns me about a fatal error and tries to save the project.

it’s a very serious problem because I work with projects with many footages and every time I reopen the project I lose a lot of time waiting for loading.

I hope I explained the problem clearly.

(i must says that premiere CC17 crash also when i try to copy and paste text in the title panel, but this for now is a minor problem)

i work with:

iMac (27-inch, Late 2012)

3,4 GHz Intel Core i7

16 GB 1333 MHz DDR3

NVIDIA GeForce GTX 680MX 2048 MB

All the footage are placed on a Qnap Nas where i enter through our internal network.

thanks