Paul Beach wrote on his blog :

There is a small problem with Firebird 2.5 SuperServer and MacOSX 10.7 (Lion)…
SuperServer will not start, and produces a crash report header similar to this

The bug is fixed in Firebird 2.5.1 but Firebird 2.5.1 is not available yet. So I have fixed the problem also in the Firebird 2.5 code and produced 32bit and 64bit builds that work properly.

Read more and the solution (Download) on Paul Beach’s Blog