To cap off the most difficult period in the history of the listed insurer FBD, it is now in the crosshairs of the National Asset Management Agency, possibly Ireland's most indefatigable litigator. And FBD appears to have no idea why.

National Asset Loan Management (Nalm), the Nama subsidiary that handles relations with its debtors, this week lodged a High Court lawsuit against FBD Insurance Plc. There are no affidavits setting out the basis for the claim and no court dates set. Nor do papers appear to have yet been served on FBD.

The insurer, which recently reported half year losses of €96 million, would not comment on the suit. Nor did Nama. But FBD’s executives are understood to be mystified as to what the dispute concerns. They could always just pick up the phone and ask the agency what its beef is, mind you.

Nalm, which has fired off more than 100 suits in the last 18 months, usually resorts to the courts to tackles borrowers with whom it has fallen out or whose assets it covets to repay debts.

FBD has engaged in property development in the past, such as at the La Cala golf complex in Spain that it is planning to sell. But it doesn't appear to be a client of Nama at all. The State agency holds no charges over the assets of FBD's property arm, whose accounts cite renegotiated bank facilities with AIB.

Is Nalm/Nama pursuing FBD over an insurance claim concerning a Nama developer? It is possible it could be a disputed claim for a burst pipe or something similar. But if so, surely Nama would have engaged in correspondence with FBD prior to traipsing down to the Four Courts.

Also, as Nama repeatedly insists, it does not own any buildings. It’s difficult to see where an insurance contract between Nalm and FBD would exist.

Nama also prefers its debtors to take their own cases when it comes to commercial disputes.

A proper mystery, indeed.