Did you upload the files using Plesk's File Manager, or another method?

Do you have SSH access? If yes, have you tried this tip from the Troubleshooting page?

osTicket Awesome uses standard permissions.

All folders should be 755 (drwxr-xr-x) and all files should be 644 (-rw-r–r–).

If you suspect that your permissions are messed up you can easily reset them.

For directories

# find . -type d -print0 | xargs -0 chmod 0755

For files

# find . -type f -print0 | xargs -0 chmod 0644

Hi Steveland, 

i tried uploading the original osticket1.17.2.zip from os ticket. extract it in plesk. 
everything works fine then. Directory 755 and files 644. 

With the awesome.zip files everything is messed up.
I think there is a presetting failure within your compressing process. 

No SSH permission here... 

Same Problem with new Release 1.17.2 :-/
Workaround with FTP makes it possible to upgrade, but I think its not supposed to be like that. 

It is not possible to embed permissions in the files. Even if I wanted to do that, it isn't possible.

I have access to a Plesk server so I uploaded the latest zip and extracted it.

I see there has been a change with the default permissions that Plesk uses. The permissions on files are correct, but the permissions on directories are missing the Write setting that osTicket needs.

If you select the main directory > Change Permissions > check Owner / Write and check Change permissions recursively it should work for you.

Thanks for letting me know about this. I will include this note for Plesk when I update the Installation Instructions.