"You had contacted Adobe Technical Support regarding Lightroom is asking for serial number.
Please uninstall the lightroom trial version and re-install the lightroom from Creative cloud app.
Please feel free to contact us back for any further issues, we are available for 24 hours a day and days a week. Good Bye!
That's the reply I got from Adobe,when I did this is showed up on the CC app as not being installed Photoshop and Bridge were also showing up on CC as not being installed so I reinstalled them as well.
BTW did you reboot after uninstalling?