my homepage and everysubpages show blank after I deleted a user, and with errors:

Unknown: Assigning the return value of new by reference is deprecated in file /header.php line 57
Unknown: Assigning the return value of new by reference is deprecated in file /class/xoopsblock.php line 464
Unknown: Assigning the return value of new by reference is deprecated in file /class/xoopsblock.php line 514
Unknown: Assigning the return value of new by reference is deprecated in file /class/theme.php line 73
Unknown: Assigning the return value of new by reference is deprecated in file /class/theme.php line 196
Unknown: Assigning the return value of new by reference is deprecated in file /class/theme.php line 248
Unknown: Assigning the return value of new by reference is deprecated in file /class/theme_blocks.php line 90
Warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected 'Asia/Chongqing' for 'CST/8.0/no DST' instead in file /Frameworks/compat/language/english/local.class.php line 176
............
too much Warnings


when I add the deleted userid the problems seems be solved, for example: be deleted the user's id is 2, then I add a line and set userid as 2, my pages come back...

but does it mean I can't delete anyuser? how can I do?

I found that lifetype modules arouses this problem, delete a user who owner a blog would cause problems, while I uninstall lifetype module I can delete users as usual.

Try cleaning your caches, ie delete the files (except index.html) in

xoops_data\caches\smarty_cache
xoops_data\caches\xoops_cache
xoops_data\caches\smarty_compile

update the module giving problems in this case lifetype.

Hopefully this would do the trick