Typically, this means that the version of the installer you are running does not match your license. For instance, if you downloaded a 2.5.0.0 installer, but you have a 2.6.0.0 license (or vice versa), you will receive this error.
Please download the right Muse version.
If this is not the case then check the copied Serial Number for extra characters due to a faulty copy/paste operation. After copying the Serial Number string please first paste it in a plain text document and check it to make sure it does not contain extra characters at the beginning or at the end of the string.