I'm not sure how to fix that issue but try creating a new team server project to see if you get the same error.
Create a package from your current project
In your current project in the top left click File > Export project package
Click the project tab > show project directory in explorer.
go in to the folder called packages and then move your projects .mpk to your desktop.
Create a new project from an existing package.
Open the modeler and click open app
set the location as disk and a windows dialog box will open
choose the .mpk file from your desktop
make sure enable team server and upload to new repository is checked
Change the name to something else and then press ok.
Then the modeler will upload your project to the team server and open it up in the modeler. From there you can click run again and it will deploy the project to a new sandbox environment.
If the same error occurs I would submit a ticket to mendix support.