We have been trying to create a form which have multiple select fields inside a field collection.
1. Second select option values depend on the value selected for first Select
2. Third selection option values depend on the value selected for the second select
This is something like conditional fields, but different from conditional field as we are using taxonomy terms.

When there is no field collection the above mentioned method work without any problem. But when the select fields are inside a field collection we are getting some ajax error as show below. Could anyone please help us how to tackle this issue

Debugging information follows.
Path: /system/ajax
StatusText: n/a
Fatal error:Cannot unset string offsets in modules/field/field.default.inc
ReadyState: undefined";