Just to add. I used to get a few of these some years back and they can be confusing if you don't understand what's going on. You will notice it said argument 2 but the problem was with ListBrowserBase which is the first argument you passed. Huh? :-) The reason for this is the way calling functions or methods are implemented in an Interface. See every time you call a method from an Interface, just like when calling a 68K library function, it needs to have the base pointer as well. Which uses some compiler magic to pass the Interface as argument 1. Now this is all hidden of course as if you had to manually pass the Interface yourself the code would look quite obtuse. And would defeat the purpose of being object oriented. This explains how passing argument 1 to an Interface method ends up as argument 2 in the actual function call. :-)

With the interface method the actual interface is argument one. Take this as an example: IDOS->Lock( file, SHARED_LOCK ) This would actually translate to: Lock( struct DOSIFace *Self, CONST_STRPTR name, LONG type ) Therefore, the name passed in is actually argument 2 even though it appears to be argument 1 in the first example. Simon

Hello again. Yeah Simon pretty much explained it. So you don't have to cast anything or think about since it's all automatic in the APICALL. Only to keep it mind when you get errors like above. It's like on 68K where the A6 register has to hold the library base to call the function off. You don't see it when coding in C. Even if it is the last register or argument in this case it functions the same as an OS4 library call. :-)