[TYPO3] Error when upgrading tt_products to newest version

[Carsten Gehling]

I am running Typo3 3.8.0, and I am trying to upgrade tt_products from
version 1.2.7 to the new version 2.3.12

I have already installed fh_library and table library.

When I press the icon "Update the extension in global.....", I get an error
page saying:

Error: Installation is not allowed in this path (typo3/ext/)

What am I doing wrong? I have checked the permissions in the filesystem for
the folder typo3/ext, and it seems to be ok.

- Carsten