After highlighting a selection of entities and relationships in a workspace, then trying to move them with mouse drag, or using left or right arrow, Toad errors out with an Access Violation.
WORKAROUND
Toggle off 'Snap to Grid' button and/or 'Snap to Object' in the toolbar when making move.
STATUS
Fixed in version 5.3. The latest version of Toad Data Modeler can be downloaded here.