When i have been browsing an topic of the vBulletin forum and then submitted login form on the top of the webpage. I received warning:

"Invalid Redirect URL (http://urlhere..)"

in AdminCP -> Settings -> Options -> "Site Name / URL / Contact Details" i have "Forum Name" set to httpS://.....

"Homepage URL" i have set to http://...

(because i want to allow all people to read forum even if their browser do not support my SSL)

this "Invalid Redirect URL" issue was fixed when i added:
into the field:

"Redirect Domain Whitelist"