What does these errors mean ?

This is my code:
[browsePanel beginWithCompletionHandler:^(NSInteger returnCode)
{
if (returnCode == NSFileHandlingPanelOKButton)
{
if (returnCode == NSOKButton)
{
if ([sender tag] == 1) {
// Templates
[[NSUserDefaults standardUserDefaults] setObject:[browsePanel directory] forKey:@"kPreferencesUserTemplateFolder"];
} else if ([sender tag] == 2) {
// Images
[[NSUserDefaults standardUserDefaults] setObject:[browsePanel directory] forKey:@"kPreferencesSaveImageFolder"];
}
}
//FreeAndNil(browsePanel);
if (browsePanel)
[browsePanel release];
}
}];
I also get a warning (I can’t explain why):
"NSOpenPanel may not respond to '-beginWithCompletionHandler:'
What Mac OS X Versions and Architectures are you targeting?
-beginWithCompletionHandleris not available before 10.6The
__Block_object_disposelinker error is a little concerning because all libraries needed for blocks should be automatically linked in.