How to show an error if there is no folder.

[eluser]pistolPete[/eluser]
You can use the PHP function is_dir(): http://php.net/manual/en/function.is-dir.php

Code:

if( !is_dir('./images/'.$foldername.'/') )
{
   // check the return value in your controller; if model returns FALSE, show an error
   return FALSE;
}
else
{
   // upload
}