1) Is there some possibility to open file saved in 5.00 with caesar 4.50??
Not really. This question comes up every other week. Use the [Search] facility.
2) In release 5.00 I've lost the main toolbar on local stress WRC 107, and I'm not able to find it again. Do you have some tips??
Use the registry editor (REGEDIT) and navigate to "hkey_current_user\software\coade inc.\caesar ii\5.00". Once here, delete the key for "local stress".