Illegal Offset when using the Multistep Nodeform module

I have a node split up into two different steps using the Multistep Nodeform module (https://drupal.org/project/msnf).

1st Step:
Entity reference using the Multiselect widget.

2nd Step:
Date field.

After selecting the entities with multiselect, and going to step 2. The following error appears:

Warning: Illegal offset type in _multiselect_build_widget_code() (line 222 of C:\inetpub\wwwroot\sites\all\modules\multiselect\multiselect.module).

The node saves just fine. However, I also noticed that when going back to Step 1, the multi select form is blank again.

Any help would be much appreciated. Thank you.