Hi, I downloaded and installed Repository Manager onto my system (Ubuntu 18.10). I initially got the same error as you. However, when I modified the folder permissions to include read and write for other users, I was able to export to my test directory. 
I'm using the 3.1.0.468 version of the Dell Repository Manager on an Ubuntu machine, and have trouble creating an ISO file. I tick the check box for the repository I want to update and click EXPORT. Regardless of what I enter as a location for the Smart Bootable ISO, I am served this error message when clicking EXPORT: 'The specified path is not accessible. Kindly check the path or access rights.' I have tried several different directories that I know I have read/write access to, and even tried with root with the same result. Anyone actually tried this with Linux?
Unable to specify acceptable path when creating bootable iso