I understand the problem, but nothing can be done about it.
Literal
Problem [topic-は] well understand, but, cannot-be-helped.
いたしかたありません (致し方ありません) is a formal/humble variant of 仕方がない ('it can't be helped'). いたし is the 連用形 of いたす, the humble form of する. The が is concessive — 'I understand, but...'