It definitely messed with the database somehow, because the database now has a corruption. I had to go to my FTP server manager outside of wordpress - restore an old backup from the previous day BEFORE I could re-access wordpress.
I then worked on it for about 2 hours (with the SmartManager plugin active) and after a while the same problem occurred - and the database was corrupted.
The next time i went into my FTP server manager renamed the plugin restored the working database again and got access to wordpress. After that i deleted the plugin and have had no problems since then.
As installing this plugin was the only change I made both times and no access was the result both times, I am pretty sure I can say it is the Smart Manager doing something to the user/customer databases.
let me know if you want more info, but i wont be reloding it as it takes a few hours to go through the restore process and that is BORING!
PS I recognise now I misread the install instrauctions which state that WOOCOMMERCE and not WORDPRESS need to be totally up to date. Can i suggest a word change at that point may prevent other users makign the same mistake. I also understand that this was may error for not checking the compatibility properly.