Did you recently install the Aerospace Blockset? You can then try to execute the following commands to reset MATLAB's path to factory conditions. Note that this will remove any user added path that will need to be manually added later. But this is one way to reset MATLAB back to its 'pristine' condition. You can try to see once you do this, if your simulation works.
restoredefaultpath
rehash toolboxcache
If the above doesn't work, there could be a chance that you are trying to pull a license from only a limited number available in the pool. In this case, you can try the following command to see if you can actually check out a license:
license('checkout','Aerospace_Blockset')
If the answer is 1, you are actually able to check out the license. But I am guessing your answer will be 0 in which case, you should get in touch with your license administrator or MathWorks support to get a better picture.
