interface A
{
};
interface B : A
{
};

After preparing the above code, executing asbuild stopped at assert.

$ ./asbuild.exe config.txt script.as x.bin
Assertion failed: t->interfaces.GetLength() == t->interfaceVFTOffsets.GetLength(), file ..\..\source\as_restore.cpp, line 4283

t->name.AddressOf()                == "B"
t->interfaces.GetLength()          == 1
t->interfaceVFTOffsets.GetLength() == 0

Thanks for the report. 

I'll look into this and have it fixed as soon as possible.

I've fixed this problem in revision 2484.

Regards,
Andreas