We usually see this error when the teacher and students are not using the same curriculum. Please verify that you are using the same curriculum and, if not, instruct your students to change to the curriculum from which the skills are being assigned.
How do I know what curriculum I'm using?:
To check this on the computer: Look for the flag in the upper right-hand corner. If you need to change this, select it for the drop-down menu.
To check this on mobile devices:
Click on the purple menu form the right-hand side, and then select Settings.
From the drop-down menu, select Settings. Look for the flag icon.