error of pcmanfm mounting a usb stick

[farinet at arcor.de]

When i push in a usb stick i'm asked

	Open in filemanger

I say yes and i get the following error:

---
Error mounting /dev/sdb4 at /media/<user>/disk: Command-line `mount -t
"ufs" -o "uhelper=udisks2,nodev,nosuid" "/dev/sdb4"
"/media/<user>/disk"' exited with non-zero exit status 32: mount: wrong
fs type, bad option, bad superblock on /dev/sdb4,
       missing codepage or helper program, or other error
       In some cases useful info is found in syslog - try
       dmesg | tail  or so
---

I see the drive but i'm unable to mount. When i'm going to the mount
point as user it's empty, going there as root i see the files and can
manipulate them.

Frankly, it's not really the way a filemanager should work. May someone
here knows, which helper program might be missing?

TIA