Updating ROM is stuck as TWRP does not see zip files

In the process of trying to install 4.4.4 on my galaxyTab 10.1, I've installed TWRP 2.7.1.0. At this point when in recovery mode I need to select the Zip to install, but none of the previously downloaded zip files are visible to TWRP. Neither under the install command nor in the file manager. I had backed up, removed caches et al. When rebooting in normal operation mode, those files are browsable. Permissions are set to 777. So I don't understand where the hang-up is?