From the text of the error message, your license only allows a certain number of users to use Image Processing Toolbox simultaneously. That many users are using Image Processing Toolbox right now. You will need to wait until one of those users is done using the toolbox. If your need is urgent contact your license administrator (probably someone in the IT department) and see if they can determine who's using the toolbox right now and ask one of those users to let you use the license.
If this problem occurs frequently, perhaps you should ask your license administrators if they can purchase more seats for that toolbox so more people can use it simultaneously.
