Please update TurboTax. Here is what you can do if
TurboTax can’t update itself: https://turbotax.community.intuit.ca/replies/3262510
If the .tt18 file still won’t open, locate the
.ttbk file with the same name (in the same folder) and change the extension to .tt18.
Then open that. By default, TurboTax puts files in a location that looks
something like this: C:\Users\yourname\Documents\TurboTax\2018
