Perpetual program reopens error: The type or namespace name 'Properties' does not exist in the namespace 'xxx' (you are missing an assembly reference?). Suppose there is a namespace space xxx how to declare how to use attributes and resources, for example: global :: xxx.Properties.Resources.sys_h;

It sounds like you are missing the 'using' statement for the required class at the top of the code file.
So, if you have the class Properties inside a namespace XXX you would add

using XXX.Properties;

at the top of any other class that intended on using it.
This may also require you adding the reference to the project, as you may have done when adding System libraries.

I also did the way you instructed but still error: The type or namespace name 'Properties' does not exist in the namespace 'xxx' (are you missing an assembly reference?)

This is likely to not fix it but I had it happen and it did. Mind you that the code looked right but I had to use the Clean then Rebuild options in the menu of Visual Studio. Remember I don't claim this will fix it as folk have a lot of bugs on their new app but this one did happen to me and it helped.

These fields you said that I've try all but not

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