Getting -> Illegal string offset 'date' in drupal_array_set_nested_value() (line 6882 of includes/common.inc)

Hello everyone,
Does anyone have an idea how to fix this error?
When I'm trying to access the page admin/bat/events - getting error

Warning: Illegal string offset 'date' in drupal_array_set_nested_value() (line 6882 of ...
/includes/common.inc).
Error: Cannot create references to/from string offsets in drupal_array_set_nested_value() (line 6882 of ...includes/common.inc).

D7 is fresh installed.