Although the error you get doesn't exactly indicate the following cause, you might try it out:
Make sure you've updated your computer fully (including SP2 if you have XP)...
Go to the
Windows update site (with MSIE!) and install every update. After that reboot and check
again the Windows update site if there are any new updates which are only visible after you've installed other updates. Repeat this process untill nothing is shown on the update site anymore.
After all that reboot and try again to access your logs. Also make absolutely sure you have the correct password for each individual encrypted log file.
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