If you get the error message ‚Version number in composer manifest of package „tt_address“ is missing or invalid‘ (or in another extension), you can follow these instructions here: https://wiki.typo3.org/Exception/CMS/1395614959
Where is written: „This happens in TYPO3 6.2 whenever an extension has a dependency on another extension which contains a file composer.json without any version number (which is actually the best practice).
Simple solution for the time being since composer is not properly supported in TYPO3 6.2 is to delete the corresponding file composer.json or to explicitly set a version number.“
There are also some bug related data, which seems to show that the issue is fixed: https://review.typo3.org/#/c/46356/
But what is when the issue is happening in TYPO3 7.6 or you are adding a version number to the file composer.json like it is stated in this bug report: https://forge.typo3.org/issues/73625, but that won’t help or you are even deleting this file composer.json and clear the cache in install tool literally 100 times and the typo3temp folder too – but the error message still occurs?
What did helped me: I uninstalled the extension, reinstalled it, but before activating it in the extension manager, I deleted the file composer.json in the tt_address extension folder.