The undo function is frozen

Hi,

I work with my Cubase 8 all the time, but today I met a problem. A project of my work, I don’t know why every time after I recorded some thing (both in MIDI and Audio recording), the undo function will suddenly be frozen and can not set any step backward, at the same time the event I’ve recorded will be block (can’t be edited or even be selected). For ex, you can see I got 251 steps in the undo history, but Undo and Redo is showing gray and can’t be used. Anyone knows what’s happen with my Cubase?

Here are the error images
Imgur
Imgur

Weilun

Hi,

I’m having exactly the same problem in one of my projects (and it’s an important one for a Jingle I’m doing)
Did you ever found out how to fix that?

Thanks!

David