This is not a bug, the problem could be an issue with the module encountered during its activiation or browser related problem.
Test to modify permissions for the module using another browser.
If the issue is occuring at sitefintiy runtime there must be an error log generated for this problem in App_Data/Sitefinity/Logs/Error.log, reproduce the problem by navigating to permissions for the module and check Error.log for error message (the latest error log is at the bottom of the file) there is a timestamp indicating the time where the error occured. Let me know what is the full error from the log.
When module built with the module builder is activated it writes all its related data in App_Data/Sitefinity/Configuration/DynamicModulesConfig.config and for permissions in /SecurityConfig.config, to ensure writing data to the config files will not encounter a problem grant App_Data folder and all subfolders read, write, modify permissions in IIS as sitefinity refers to the configuration files when working with dynamic modules.
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