Difficulties faced by entity when applying a change in accounting policies.

Accounting policies are the specific principles, bases, conventions, rules and practices applied by an entity in preparing and presenting financial statements.
Changes in accounting policies is dealt with in IAS 8

Difficulties faced by entity when applying a change in accounting policies are:
When it is impracticable to determine either the period — specific effects or the cumulative effect of the chance for one or more prior period presented.
Such difficult will lead to a limitation when an entity is either applying prospective or retrospective change in accounting policies.