SORRY, I SOLVED THE PROBLEM 5 SEC AFTER I POSTED IT... For some reasons the cache cleaner directory did not have write permission... Set to "read/write and all problems gone... I should have checked that earlier... I leave the description below for the next dumb to read and think...

SOLVED:

I installed CacheCleaner as usual without problems. I then enabled "clean cache upon save - back end". From then on ANY action in the back end started throwing the following warning:

Warning: file_put_contents(/Applications/XAMPP/xamppfiles/htdocs/siteName/plugins/system/cachecleaner/lastclean.txt) [function.file-put-contents]: failed to open stream: Permission denied in /Applications/XAMPP/xamppfiles/htdocs/siteName/libraries/joomla/filesystem/file.php on line 298
Invalid Token"

I then switched off the option "clean cache upon save - back end" because I thought it might have anything to do with the issue. NO change.

I looked for the "lastclean.txt" but there is NO such file in that directory! (I know from a previous installation that in that other installation the file exists, but not in this installation...?!)

Then I logged out at the end of the day............ and now CAN NOT LOG-IN anymore........

When trying to log-in, first, for a split sec, the following message appears on a white page before the log-in screen with the cache cleaner warning on top is shown again:

file_put_contents(/Applications/XAMPP/xamppfiles/htdocs/siteName/plugins/system/cachecleaner/lastclean.txt) [function.file-put-contents]: failed to open stream: Permission denied in /Applications/XAMPP/xamppfiles/htdocs/siteName/libraries/joomla/filesystem/file.php on line 298

Warning: session_start()[function.session-start]: Cannot send session cookie - headers already sent by (output started at /Applications/XAMPP/xampfiles/siteName/libraries/joomla/filesystem/file.php:298) in /Applications/XAMPP/xamppfiles/htdocs/siteName/libraries/joomla/session/session.php on line 539

Warning: session_start()[function.session-start]: Cannot send session limiter - headers already sent by (output started at /Applications/XAMPP/xampfiles/siteName/libraries/joomla/filesystem/file.php:298) in /Applications/XAMPP/xamppfiles/htdocs/siteName/libraries/joomla/session/session.php on line 539

Any suggestions??

Quite urgent as I am cut off at the moment...

Thanks !!

Tom

P.S.: installation is on a local host still (running Joomla 1.5.19, XAMPP on Leopard, PHP 5.2.9, Apache 2.2.11, other Joomla installations on same machine work all without any problem)

P.S.S.: to see what happens, as the lastclean.txt does not exist in the specified directory, I first created an empty file with a proper text editor and put it in that folder - NO change. Then I temporarily copied a lastclean.txt file form another Joomla installation (containing a 10 digit number) into the directory - also NO change.