try to kill your java process Ctrl+Shift+Esc (taskmanager)
or the .lock file (<your project>.mpr.lock)
The first thing I would check is to see if the Java process you had up before the modeler crashed is still running. This can be found by hitting ctrl-shift-exc and going to the program manager. Look for a Java process that may be running still. This is the local Mendix runtime and if there was a crash it may not have shut down correctly. Kill that process and try re-running your app.
Alternatively, it possible that you have a file in the 'Deployment' directory open in another program? For example, one of the theme css files open in a text editor? That can cause the issue you see. Sometimes I have the theme zip open in a file viewer and get the same issue.
If you do not have local data that you need, you could also simply delete the 'Deployment' folder from your project home. That folder is completely rebuilt every time you hit the 'run locally' button. However, your data also lives here so you would lose that if you took this option.
I guess I should have tried rebooting my machine right away. This seems to have solved the issue I ran into. Thanks for your swift responses on my thread. Much appreciated.