Dear @asmecher,
Thank you for your mail. Yes, it is more easy to work with older domain, but, I cannot solve the problem with the database. Now I received an error with older database and some articles wont open. I really dont know what to do next. Now I made subdomain, instal new OJS 2.4.8.1 and new database and try to import issues. I have got some problems, but wait answer from your colleagues about importing. You can read it our conversation on this thread.
If you have some advice for my old database, how to solve the problem and upgrade to OJS 3.0.2 feel free to give me advice. I am really empty with an idea what to do and now is the time when I will start to receive new articles for new issue. I am ready to continue with correcting this error because many of my colleagues which I know work under OJS 2.4.8.1 and afraid to start with OJS 3.0.2 because they read a lot of problems with the upgrade.
I am looking forward to hearing proposal from you.