TYPO3 Core

After Updating to 4.1 AND doing the database-updates (seems not to happen without db-updates!) opening arbitrary pages returns:
-----------------------------------------------------------------------------------------
Warning: reset() [function.reset]: Passed variable is not an array or object in /usr/share/webapps/typo3/4.1/typo3/sysext/cms/tslib/class.tslib_content.php on line 2995

Warning: Variable passed to each() is not an array or object in /usr/share/webapps/typo3/4.1/typo3/sysext/cms/tslib/class.tslib_content.php on line 2998

Warning: Cannot modify header information - headers already sent by (output started at /usr/share/webapps/typo3/4.1/typo3/sysext/cms/tslib/class.tslib_content.php:2995) in /usr/share/webapps/typo3/4.1/typo3/sysext/cms/tslib/class.tslib_fe.php on line 2898
-----------------------------------------------------------------------------------------

Interestingly after deleting all cache the first page called shows up correct, but the second and all further are not displayed (only above error appears).

Locally installed extensions:

addressgroups
arotea_loginbox
chc_forum
ch_handbuch
csh_de
da_newsletter_subscription
de_phpot
dir_listing
dkd_imagemap
external_pageset
galileo_atom_export
goof_fotoboek
https_enforcer
iframeflexform
iim_feuserspasstype
ipmaskmountgroups
julle_events
julle_feedit
kickstarter
lastupdate
lz_table
macina_searchbox
make_printlink
mbl_newsevent
mf_pagetitle
mit_download
naw_securedl
newloginbox
n_extkeywords
nf_downloads
nuxos_randompassword
pil_mailform
quickpoll
realurl
sp_directory
sr_feuser_register
sr_static_info
static_info_tables
sys_stat
sys_todos
sys_workflows
tt_address
tt_news

(issue imported from #M5190)