This error can appear if there are changes to the project structure outside of the Mendix Model itself (theme, javasource, etc). To resole those issues, you can download TortiseSVN v 1.7 which will give you details about issues outside of the modeler.
Since you are just doing a training project, your issue might not be due to conflicts from intentional project changes. Is it possible the drive you have the project installed on a shared or network drive? Perhaps one with an automatic backup or a dropbox-like auto-upload feature? I have seen those setups cause file conflicts. If so, perhaps install your projects locally.
I fixed the problem. The app runs perfectly now. The error was in the way I modeled some logic using microflows. It still remains a question why the Changes dock couldn't be opened when I had a merge conflicts.
delete the whole project folder and download it again.
You might lose some work but seeing as its the training, probably not too bad :D
This is the Changes dock. Is it empty like in this screenshot?
Maybe excluding the page that is giving the merge conflic from your project before updating can help?