I can't open my project

If you encounter the warning "The project file is incompatible with this version of HeavyM." when trying to load a project in HeavyM, it can be due to different reasons.

The project is not compatible with this version of HeavyM

Here's a little overview of compatibility in HeavyM 2:

• HeavyM 2 respects backward compatibility: if you have created a project with an older HM2 version, you'll be able to open it in a more recent update. For instance, a 2.11 project can be opened in 2.13. 
  It is possible though that due to major updates on some features, your project has encountered minor changes. But we try to guarantee a full compatibility as much as possible and if not we'll warn you in the release notes or relevant Help Center article.

  Note: HeavyM 2 is backward compatible with all HM2 versions, however it is NOT with HeavyM 1. The compatibility was broken when switching between HM1 & HM2, thus HeavyM 1 projects don't work in HeavyM 2. If you wish to access an old project and don't have access to HeavyM 1, please contact the support.

• HeavyM 2 doesn't guarantee forward compatibility: if you have created a project with a recent update of HeavyM and try to open it with an older update, it'll most likely not work. For instance, a 2.13 project is not guaranteed to work in 2.11. 

  Very Important Note: what defines the version of a project is where it was last saved. So a project created in 2.11 but saved in 2.13 is now a 2.13 project! That is why it's important to make copies of your work, for instance if you want to run some tests for a big project on a newer version, or if you work collaboratively and your colleague is using a different version of HeavyM. 

  If you do save by mistake once, you can find a previous copy of your project in the "Backups" folder (see below).

The project file is corrupted

Your project file could have been corrupted because of an issue during a save. It's usually very rare, but the probability can increase if, for instance, you have the habit of not turning off your computer correctly while the software is still open (please don't do that), or if you were saving your project on an external drive and disconnected it during the save.

If the .hm project file has a size of "0 Ko", then it is definitely corrupted and can't be saved. However, as of HeavyM 2.13.6, you can find a copy of the .hm in its second to last saved state in the “Backups” folder of your project folder. Another copy is also added in "Documents\HeavyM\Project Backups" (since 2.13.9). 

More details about this backup can be found here.