Hello Sam,
Please run the Instance Configuration Wizard from the passive node, which the error indicates it can't configure, and the install should complete without any further errors. If this fails to work please open a support case.
In most cases you should have no issues installing LItespeed to a cluster. However, If you have any problems with the Instance Configuration Wizard during installation – skip the wizard (press Cancel) and complete the installation.Then after installation completes run the Instance Configuration Wizard from the Start menu and complete it.
Hope this helps,