Slideshow major problem

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Hello,
We are having a problem with the slideshow that comes with C5. The slideshow completely disappears for unknown reasons. Looking in the forum for answers, found that on an older version of C5, the answer was to set the file permissions on each file individually for the Guest. When viewing the Access & Permissions on a file found this error:

Fatal error: Class 'UserInfoList' not found in /home/adminuser/prod/htdocs/concrete/tools/files/permissions.php on line 117

The other image files do not have an issue showing up in the browser, however they also have the above error. All of the image files in our File Manager have the above error.

Can anyone confirm that this is a bug for C5 version 5.6.1.2? If not a bug, what is the fix for this version?
Thanks!