Sometimes the update download does not complete successfully, causing Oasis to fail on startup. To fix this, you must delete the .oasis folder and then relaunch Oasis so it can download the latest update again. Here are operating system specific links for instructions on deleting your .oasis folder.
Deleting the .oasis/lib Folder on Windows XP
Deleting the .oasis/lib Folder on Windows Vista
Deleting the .oasis/lib Folder on Windows 7