NSInvocation and argframe errors

[e.sammer]

hello all...

i'm using NSInvocation to pack a bunch of selectors into a dictionary 
(as values) using strings (xml element names) as keys. when the parser 
executes, i'd like to have something like:

while (currentNode = [currentNode next]) {
  [[selLookup objectForKey:[currentNode name]] setArgument:[currentNode 
content] atIndex:0];
  [[selLookup objectForKey:[currentNode name]] invokeWithTarget:self];
}

(this is a _highly_ simplified example)

what i'm getting is, at runtime:

Uncaught exception NSInternalInconsistencyException, reason: Runtime 
incorrectly configured to pass argframes

i have GNUstep compiled against ffcall. am i doing something that is not 
"normal?" i've done similar things on mosx with little trouble, so i 
just assumed it was standard usage of NSInvocation (ala NSTimer).

any help would be greatly appreciated.
--
e.sammer <eric@lifeless.net>