There can be various possible reasons for such an error like incorrect path, some garbage cache value. You can go through the following steps and then restart Simulink and retry opening the model:
- Execute the following command from MATLAB terminal: ‘restoredefaultpath’
- Try to clear the cache with the help of following command: ’rehash toolboxcache’
- Then execute this command: ‘savepath’.
- Also, ensure that the ‘Simulink cache folder’ under the Simulink Preferences is blank. Please refer the following image: