Hi @atarix
The second messages mean that your files in the files folder could not be migrated to the right position – it seems that the access permissions are not right. Could you double check the permissions on your files folder – maybe allow everything for the moment you are upgrading – and try again, but do not forget to use your back-up i.e. original files folder (and not the one after an upgrade trial!).
For the first message: How does the code line 1983 and/or 2141 (the messages are pointing to) looks like in your installation? – I do not see that number here: ojs/Upgrade.inc.php at ojs-3_0_2-0 · pkp/ojs · GitHub 
Thanks!
Bozana