I have installed com_multisite. All patch are applied.
I create a slave site and after that when I try to open /multisites/xxxxxxxxxx/installation/
receive this error
[Wed Jan 20 03:11:15 2010] [error] [client 82.147.xxx.xxx] PHP Fatal error: Allowed memory size of 67108864 bytes exhausted (tried to allocate 16 bytes) in /var/www/vhosts/xxxxxxxxxxxx/httpdocs/libraries/joomla/error/exception.php on line 117

Which platform are you using ? (I suppose Unix with Symbolic Link allowed)

Do you have such problem only with one slave site or when you try create any slave site ?

Do you have such problem when you follow the tutorial video 9 or CP-04 ?
www.jms2win.com/tutorial#jms12x-9
www.jms2win.com/tutorial#jms12x-CP-04

Which version of Joomla are you using ? (1.5.15 ?)

If Joomla 1.5.15 then this is probably due to an object that Joomla want to report in error and for which it contains "recusive" reference inside the object.
In this case, the Joomla exception processing may failed due to this recursive object reference that make PHP loop when trying report the error.

The only method that I know to identify the reason consists in modifying the Joomla statement 117 to replace the statement with debug_backtrace by debug_print_backtrace to report the error upon screen.

If you want that we debug the reason in your environment, you can also order our billable support at www.jms2win.com/download?page=shop.produ...35&category_id=1

I found where is the problem.
It is my mistake.
When I create a new page I have added like domains
www.xxxxxxxx.com
xxxxxxxxxx.com

But I try to access the site at htttp://mastersite.com/multisties/xxxxxx.com
When I add and htttp://mastersite.com/multisties/xxxxxx.com
to site addresses all start to work.