I have tried to reproduce the described scenario, but to no avail. I am afraid that I can only assume as to what the configuration of the controls is.
Without any further information, I can only suggest checking if the ViewPaths of the ImageManager are properly configured (using slashes (/): '~/
Folder1/SubFolder1') and if there are any errors that have been raised in the browser's console. Should you be using a custom content provider, may I ask you to verify if it is not the one causing the problem?
Another possible reason for the issue to appear could be if you have customized the built-in Image Manager Dialog and have not updated it to match the control's version. It is very important that the used External Dialogs are from the same version as the control.
Should none of the above suggestions result in the expected behavior, in order to further investigate the issue, could you, please, provide us with additional information regarding the browser in which the problem appears and its version? Also, is the latest version of the controls you are referring to 2013.2.611? It is of importance to know if you have implemented a custom content provider, as well. Should the problem persist, could I ask you to prepare a sample fully-runnable project, isolating the issue
, so that we can further delve into the issue?
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