This is a tutorial on how to fix the files followed by the SAI "Failed to open canvas" error.
I renamed some of my files via the file browser where you open your files in SAI. It messed up the files. I did some very tedious research and found there was little direct information on the matter, so I made this tutorial.
If you have any questions- please ask!
WARNING: This may or may not help you. This is just what helped me, and I hope it may help others.
EDIT: I've gotten pretty good feedback with how this has helped more than failed. Some people found this didn't work for them and were kind enough to leave their way of fixing the issue....
-Ok I was able to open my file after this error, but this solution did not work. I will give my own so that people can see it when they have this problem.
-First of all saving as a psd is a MUST ok, if you want your files to be alive it's compulsory. I never saved as sai as a habit I made and honestly it just saved my life.
-Ok the files will almost always open in photoshop. Unless its full on corrupted. Mine always open tho. What I did was, if your file has a lot of layers try to merge as many as you can to not affect your work. Secondly create a new file in photoshop with the same canvas size and drag all the layers into the new picture. Save the new file and open it in sai. It works.
-If it still doesn't try reducing the size of your canvas. You know if u have like 10kx10k it's prolly the comp issue haha xD
-I found a way to fix it but it's kind of crazy...
-You have to make a new page to work on, make it nice and big. Then, use the square looking "selection" button. Make a giant rectangle to fill up the new blank page.
-You can open up your pictures in something else, like paint. Right click and copy the picture, then paste it into this "selected area" using the Edit tool at the top of paint tool sai.
-And when you save it, you can save it as .sai and it should stay that way. Problem solved!
-Hope this helps...