export png error

when I export>export as>png

"the operation cannot complete because of an unknown error. [!now]" window pops up

export>save for web

"Could not complete this operation. An unknown error has occurred." window pops up

so I have to use photoshop for exporting png.

I read this 

https://community.adobe.com/t5/illustrator/illustrator-showing-quot-the-operation-cannot-complete-because-of-an-unknown-error-now-quot-error/m-p/9887678

and change UXP to 00UXP but still have a problem.

I remove with adobe creative cloud cleaner tool and reinstall it but still have a problem.

I'm using window 10

Its latest version

No 3rd party plugins

Wacom tablet is the only additional hardware I use

I'm only using adobe fonts. noting on the internet download.

and all fonts are fine

I tried as soon as restarting the computer every time.