Cryptic DMD error

[Lars T. Kyllingstad]

Can someone with knowledge of the DMD source code please explain this 
error message for me?

dmd: glue.c:652: virtual void FuncDeclaration::toObjFile(int): Assertion 
`!v->csym' failed.

I had a look at the DMD source to try and make some sense of it myself, 
but didn't succeed. I am using the latest DMD, 2.029.

I am in the middle of porting a library from D1 to D2, and as there is 
no mention of a file name, let alone a line number, I find it hard to 
narrow down the cause of the error.

Thanks,

-Lars