I have all the required modules loaded, but this one fails :-(

root@palais:/lib/modules/2.6.19.1# lsmod | sort
Module                  Size  Used by    Tainted: P
arc4 864 0 - Live 0xc0222000
ath_hal 222016 3 ath_pci,ath_rate_sample, Live 0xc0197000 (P)
ath_pci 83152 0 - Live 0xc0226000
ath_rate_sample 10464 1 ath_pci, Live 0xc0159000
cifs 230784 0 - Live 0xc015d000
cls_fw 3264 4 - Live 0xc01cf000
crc_ccitt 1024 1 ppp_async, Live 0xc00e1000
ehci_hcd 27248 0 - Live 0xc0060000
ext2 40304 0 - Live 0xc0087000
ext3 101968 1 - Live 0xc00bb000
fat 43568 1 vfat, Live 0xc0069000
ip_conntrack_amanda 1744 0 - Live 0xc0137000
ip_conntrack_ftp 4144 1 ip_nat_ftp, Live 0xc012e000
ip_conntrack_h323 35168 1 ip_nat_h323, Live 0xc0145000
ip_conntrack_irc 2864 1 ip_nat_irc, Live 0xc0131000
ip_conntrack_pptp 5520 1 ip_nat_pptp, Live 0xc013d000
ip_conntrack_sip 3920 1 ip_nat_sip, Live 0xc0140000
ip_conntrack_tftp 1648 0 - Live 0xc0135000
ip_nat_ftp 1632 0 - Live 0xc00df000
ip_nat_h323 4864 0 - Live 0xc012b000
ip_nat_irc 960 0 - Live 0xc0133000
ip_nat_pptp 2224 0 - Live 0xc0142000
ip_nat_sip 2368 0 - Live 0xc014f000
ipt_ECN 1472 0 - Live 0xc0113000
ipt_LOG 5024 0 - Live 0xc021f000
ipt_TOS 832 0 - Live 0xc0125000
ipt_TTL 896 0 - Live 0xc0129000
ipt_ecn 1056 0 - Live 0xc0111000
ipt_ipp2p 7072 1 - Live 0xc00f2000
ipt_layer7 10032 2 - Live 0xc0117000
ipt_owner 832 0 - Live 0xc00ee000
ipt_recent 5088 3 - Live 0xc010e000
ipt_time 1632 0 - Live 0xc0123000
ipt_tos 544 0 - Live 0xc0121000
ipt_ttl 768 0 - Live 0xc0127000
jbd 54896 1 ext3, Live 0xc0075000
nls_base 4608 3 cifs,vfat,fat, Live 0xc0054000
ppp_async 9664 0 - Live 0xc00e3000
ppp_generic 20768 1 ppp_async, Live 0xc0107000
sch_hfsc 16256 1 - Live 0xc021a000
sch_red 4288 0 - Live 0xc0213000
sch_sfq 4064 4 - Live 0xc0216000
scsi_mod 67808 2 usb_storage,sd_mod, Live 0xc00f5000
sd_mod 12240 2 - Live 0xc00d5000
sha1 1536 0 - Live 0xc0218000
slhc 5504 1 ppp_generic, Live 0xc00e7000
switch_core 5120 1 switch_robo, Live 0xc0084000
switch_robo 4016 0 - Live 0xc005a000
uhci_hcd 19280 0 - Live 0xc00ad000
usb_storage 27152 1 - Live 0xc00b3000
usbcore 103584 4 usb_storage,ehci_hcd,uhci_hcd, Live 0xc0092000
vfat 8512 0 - Live 0xc005c000
wlan 168480 10 ath_pci,wlan_xauth,wlan_wep,wlan_tkip,wlan_ccmp,wlan_acl,ath_rate_sample,wlan_scan_sta,wlan_scan_ap, Live 0xc01d8000
wlan_acl 2816 0 - Live 0xc0156000
wlan_ccmp 6432 0 - Live 0xc0153000
wlan_scan_ap 3136 1 - Live 0xc0151000
wlan_scan_sta 9696 0 - Live 0xc0139000
wlan_tkip 10944 2 - Live 0xc01d4000
wlan_wep 4736 0 - Live 0xc0203000
wlan_xauth 480 0 - Live 0xc01d1000
xt_MARK 992 16 - Live 0xc011f000
xt_helper 832 0 - Live 0xc00ea000
xt_length 736 5 - Live 0xc0115000
xt_limit 1248 1 - Live 0xc00ec000
xt_mac 736 0 - Live 0xc011b000
xt_mark 640 16 - Live 0xc011d000
xt_string 896 0 - Live 0xc00f0000
root@palais:/lib/modules/2.6.19.1# insmod ppp_mppe.ko
insmod: cannot insert `ppp_mppe.ko': Success (19): Success
root@palais:/lib/modules/2.6.19.1#

On another router a slightly different error occors:

insmod: cannot insert `/lib/modules/2.6.19.1/ppp_mppe.ko': Invalid parameters (19): Invalid argument

Any clues?