Short answer: Contact your Matlab IT administrator. At the very least you'll need to generate a new license file in your mathworks.com account.
For an SNU (Stand Alone Named User) license, Matlab is looking at the string you type in when you log on, then comparing it against the username on the license. If your username was changed after the installation, it will throw that fault when you try to log on. This could also be the case if you've inherted a computer from a former employee but the license hasn't been updated yet.
If multiple people at the company use that one computer, you can consider switching to a DC (Dedicated Computer) license. The DC license doesn't allow for multiple Matlab versions to be installed, but it does allow you to skip the username check which is needed for shared machines. Switching to a DC license requires a bit of work in your mathworks.com account, but is easy to do so long as your maintenance is paid up.
