Painter 2020: Insufficient disk space to open new picture

OS: Windows 10

PC: Microsoft Surface Pro 6 i7 8Gb

ISSUE: error message when opening .RIFF file: Insufficient disk space to open new picture

ISSUE: error message when opening .PSD files saved in Painter 2020

All, when I try and open a .RIFF file I've created in Painter 2020 I get the above error message. I also get the following error message when trying to open a .PSD file created in Painter 2020: The file is not in the Adobe Photoshop format.

If I then try to open a .PSD file created in Photoshop, no problem. The PSD created file is more than twice the size of the .RIFF file so it can't be a memory issue. I suspect that Painter is corrupting files when saving but I don't know, in any case this issue is making Painter 2020 un-usable as it happens almost every time regardless of file size.

I'm now at the point of wanting my money back unless this can be fixed asap.

Anyone?