When I try to open a folder it is saying failed to load main classed manifest attributes why is this

Which folder do you mean? If I am right, you mean that java .jar file.

I am not very good with java application, but I know the cause of your problem, it simply means the java .jar file is not made/developed to run on the system or as an application. Perhaps it for a browser or another application. That's all what I know. I don't have much idea about "java midlet files" or "manifest attributes..."

Please don't mind, I just want to help you sort out the problem and narrow down your troubleshooting measures. Thanks.

I wish you good luck.