Have you tested with all addons disabled (community/Marketplace) ?
This issues has been reported during SU5 Configure button not working in Aircraft Selector menu - SU5 Beta 1.7.6.0 - #31 by ShadowGKR and culprit can be an addon.
If you have //42 addon, there is an updated version that fix it: Configure button not working in Aircraft Selector menu - SU5 Beta 1.7.6.0 - #51 by runshotgun