I have moved your question to Photoshop Lightroom as the Lounge is not for technical questions. If you find this is not the correct forum please let us know and we'll move to another Lightroom forum.
No you are not being forced to upgrade. I hate these conspiracy theories.
You have a license issue, where Lightroom cannot find the license information for Lightroom 5.7 it was expecting to find. It is asking for your serial number of Lightroom 4 or earlier; and then your serial number for Lightroom 5.
If you cannot find these, perhaps this document can point you in the right direction. Find your serial number (You also need a better system of keeping track of ALL of your serial numbers, not just Lightroom)
You can also look for the serial number file somewhere on your computer as given in this document: Where to find preference files for Adobe Photoshop Lightroom 5
Thank you kindly for your reply.. I am now able to get in. I am VERY relieved...
And for the record, I'm not a conspiracy theorist.. maybe just not as smart as you, which is why I came to the forum for help. oh.. and I found the serial number.. Missed it the first time.