WD My Cloud Unable to access device. (500) error! Worked great then just stopped! FW V1.03.41

Does the problem happen while doing remote access, local access, or both? You can try some of the suggestion on the following link.

http://community.wd.com/t5/WD-My-Cloud/HOW-TO-Troubleshooting-Remote-Connectivity-Issues/m-p/617261/highlight/true#M1130