There can be several different reasons why the OASIS client fails to receive an update from the database. The core reason is usually that OASIS is not able to write to its update folder (the .oasis folder). There are several reasons this can happen.
If for some reason the update process is interrupted (ie the wireless network drops for a second, the internet disconnects, etc), the .oasis/lib folder will contain an incomplete copy of the latest release which is not enough to start the program. You will need to delete the .oasis/lib folder to force OASIS to use the base installation in the Program Files directory to download a fresh copy of the latest update.
In some cases, especially with Roaming Profiles enabled, there can be permissions issues where OASIS is not able to write to the .oasis folder for several possible reasons. A common solution is to simply redirect the .oasis folder to another location, such as "C:\oasisboot", a local folder where the user would definitely have permission to write to. You would need to delete the existing .oasis/lib folder, then redirect the folder to another location using the document below.
3rd Party Applications
There are some 3rd party applications that are meant to protect or backup the system from viruses or other changes that can prevent OASIS updates. One example is Carbonite Backup. Another is Trend Micro Antivirus. You would need to exclude the .oasis/lib folder from backups or scans so OASIS can properly receive updates.