How do I open projects in Unity 2018.3 and older using Floating or Build Server licenses?

Symptoms:

• I am using Floating Licenses or Build Server Licenses.
• I am attempting to open a project using 2018.3 or older, such as 2017.4 or Unity 5.x.

Cause:

Editor versions prior to 2018.4 are not supported with Floating or Build Server licenses.

Resolution:

It is recommended that you upgrade your projects to at least 2018.4 in order to resolve this issue. 

If this is not possible, please contact your sales representative about acquiring licenses specific to these older editor versions.