I've done quite a bit of googling and can't seem to find any information on this error, so I'm going to assume it's not a common one.
The error is:
Notice: Undefined property: views_handler_relationship_broken:: $alias in EntityFieldHandlerHelper::query() (line 84 of /MYPATH/sites/all/modules/entity/views/handlers/entity_views_field_handler_helper.inc).
A bit of information about my set up, I've been using Views to show a list of my Drupal Commerce Product displays, set up similarly to Commerce Kickstart where you have the Product Display that references the Commerce Products via the SKU. This error arose shortly after removing some fields relating to a relationship the view was using, as these fields no longer exist they cannot be re-added.
I've cleared the views cache, the site cache, to no avail. Is there any kind of database entry that may be referencing this particular relationship still?