Bob03 on "Setup fails - Unable to find the wrapper "tcp""

I've been struggling to install Zenphoto on a new host. I got most of it working but I kept getting
“Zenphoto has detected a change in your installation. The script functions-basic.php has changed. The change detected may not be critical but you should run setup at your earliest convenience.”
Then, when I attempted to run setup:
“Warning: file_exists(): Unable to find the wrapper "tcp" - did you forget to enable it when you configured PHP? in /var/sites/l/[domain]/public_html/ZenGallery/zp-core/setup/index.php on line 27
Fatal error: session_start(): Failed to initialize storage module: memcache (path: /var/sites/l/[domain]/public_html/ZenGallery/zp-data/PHP_sessions) in /var/sites/l/[domain]/public_html/ZenGallery/zp-core/setup/index.php on line 32”
In the end, I assumed I'd done something wrong in the set-up. So I copied my /albums folder somewhere safe, deleted the entire installation folder and started again from scratch. The MySQL database was left as-is.
I downloaded the latest version (1.4.9), un-zipped it into a new installation folder and FTP uploaded this to my web-space. Following the installation instructions, I navigated to my gallery folder but the set-up script again crashed with the identical warning and fatal error messages
Line 32 of index.php = “$session = session_start();”
The script has executed the lines immediately before this to create /ZenGallery/zp-data/PHP_sessions. It hasn't got as far as asking me to input my database details.
What am I doing wrong?