AutoScroll - problem makeing Gallery(image picker)

Hi I have a confusing problem with the Autoscroll implementation in my own app. I Want too set up a image gallery and when the debugger gets to the part of the code

 if (! [thumb isMemberOfClass:[ThumbImageView class]]) continue;

i get an error

Undefined symbols:   ".objc_class_name_ThumbImageView", referenced from:
      literal-pointer@__OBJC@__cls_refs@ThumbImageView in Gallery.o ld: symbol(s) not found collect2: ld returned 1 exit status

and I dont know what this means Has anyone meet with this kind of error.It might be the class implementation but i don't know how to implement it. I have just #import-it into my .h file

if there 开发者_如何学Cis some other example of an image gallery please send me a link.I need to learn how to do this.

I've got the problem.It was the Executable. Works with IOS 4.0 and above :)