Error when using photoshop 2025 26.1

Hi, thanks for reaching out to the Adobe Community!

Are you referring to the Grey block in the middle of the screen or something else? If it's something else, could you elaborate on the error? 

If you are talking about the Grey block and you're getting that while painting with the Brush tool, try disabling the option to Use Graphics Processor from Photoshop by going to the Edit menu, then Preferences, then Performance. Once done, quit & relaunch Photoshop to check if it helps.