The some 'internal error' in this Java decompiler

[kalksdlkdsa]

I want to decompile some file .jar, but when I open some file .class in this, it show this error:

// INTERNAL ERROR //

What the error mean?

[Sinsify]

I got the same error

[kalksdlkdsa]

oofs

[kalksdlkdsa]

But some file .class show the code, some show the error

[kalksdlkdsa]

I think that is that file .class is incompatible of this Java decompiler or something like that (or the decompiler has some error)