There is a difference between reload errors and reload warnings.
If there is an error, the reload task will be cancelled and your .qvw will no be updated.
If there is a warning, the task will be completed.
I found warning just when a step in the reload task takes a very long time to complete. For example, before loading a table from the database, I had to call a stored procedure. This procedure took a very long time to complete, without any message to qv server. During this time, a warning is created.
You can check this post http://community.qlik.com/message/61456 that describes the same situation.
Hope this helps,