I have several old FB licenses for sites that have been using scripts for years. Some are now throwing up the alert that "FloatBox is licensed software".

Have old licenses lapsed?

Floatbox is no longer licensed - it's open source and free. Just install the latest version, and all warnings will disappear.

And no, the old licenses never lapse or expire. If nag screens are showing up it's because the pages are no longer running under the licensed domain or the Floatbox installation has changed and the license keys are not correctly installed.

Mr. Gromit is correct: it's time to upgrade to open-source Floatbox - a quicker and more beneficial task than futzing around with problems in obsolete and unsupported software.