Hi folks!
I am hoping one of you lot may be able to assist...
Stupidly worked on an old laptop, saving files to an external usb for portability while the kids where doing schoolwork... suddenly two of my latest files are un-openable, converted miracuriously to .skb files. Typicaly, to my horror i realised i had not copied these to my pc for a couple of days...
I was working in sketchupv8 at the time on a win7 laptop. Noticed there was an issue as soon as i tired to access the file again from sketchup2016/2020 on a w10 machine.
What i have done:
It affected two files, i manage to open one in v8 by changing file extension to .skp on the laptop, i copied this and savedas a duplicate.. then the two original .skb files that had been visible on the drive disapeared all together. I only have this single copy now. Luckily, they both where similar file regards content.
As it opened again on the laptop post problem.. i thought great i had solved it, but when i tried on the PC on sketchup 2016 and 2020 and both failed again to open. .. went back to laptop and no joy at all now! unable to open it in v8 either.. argh!
The error i get is 'unexpected file format' however i have also seen an error about exceeding file length occasionally.
I am running a file recovery on the portable disk, but in the meantime if anyone has a magic fix i would really appreciate it! As i managed to open it once.. i thought i could do it again, but multiple tricks down the line and nothing 
I have seen some post comments about MacOS might be worth a shot?