vB_XHTML_Ready is not defined

[IT_Smart]

I received the following error message in the google console, I researched it but I don't find the solution yet:
vbulletin-postbit.js?v=423:11 Uncaught ReferenceError: vB_XHTML_Ready is not defined
at vbulletin-postbit.js?v=423:11

[Wayne Luke]

Please upgrade to vBulletin 4.2.5. Note that it requires PHP 5.6.0 through 7.1.X and MySQL 5.5.8. Does upgrading solve your problem?

[IT_Smart]

Is this the only way to solve it?

[Wayne Luke]

vBulletin 4.2.5 is the only supported version of vBulletin 4.2.X. The vBulletin 4 series is end of life.

[IT_Smart]

How can I upgrade my current vBulletin version to vBulletin 4.2.5 version? Could affect these changes in my app? What factors should I consider?

[Wayne Luke]

From our standpoint -

1. Close your site.
2. Create a database backup.
3. You would upload the vBulletin 4.2.5 files and overwrite your existing 4.2.3 files.
4. You would then run the /install/upgrade.php file.
5. When it is done, you would delete that directory.

If you have third-party addons or a custom style, you would have to take these into account. Your addons would have to be upgraded to PHP 5.6.0+ or 7.1, whichever you use if they haven't been. Your style may have customizations that prevent template mergese. However, it is a minor version upgrade with bug fixes so the disruption should be negligible.

[IT_Smart]

If my issue is only on the mobile version, Is this necessary the upgrade?
Just to I need make sure.

[Wayne Luke]

If you want the mobile version to work, then the upgrade is necessary.

[IT_Smart]

OK, Thank you for your help.
I'II prepare the backups to the upgrade.