Symptoms

When trying to open FlexiLayout Studio project the error message "An attempt was made to access xxx.fft past its end." appears.

Cause

This error means that something must have happened such as a crash or some type of interference that occurred while the FLS project was saving or in the process of doing something and the FLS project became corrupted. 

Resolution

Try to recreate the project manually from a previous backup from the <Project>Templates folder inside your project folder.

For example:
​
In Red box there are the "corrupted" .ftt and .ftd files
In Green, the latest backup copied from the Backup folder
Just delete the Red ones, and rename the green ones removing the "_n" postfix part.

Unfortunately, in the case, there are no .afl files or backups were created it's not possible to restore the project.

Additional Information

How to restore a FlexiLayout Studio project from .afl file?