10.7 clients unable to connect to legacy NAS and AFP devices

In Lion Apple disabled older, less secure protocols like DHCAST128.  This has caused problems with older NAS devices running AFP and some Novell servers.

Most manufactures have released updates to resolve this problem but there is also a way to re-enable the protocol from the command line.

Here are the instructions from Apple's KB:

Lion maintains a list of authentication methods that are not allowed. These are the older, less secure authentication methods. You may need to enable one or more of these methods to support legacy devices or protocols.

Open Terminal.
Execute the following commands:

sudo chmod o+w /Library/Preferences
sudo defaults write /Library/Preferences/com.apple.AppleShareClient afp_host_prefs_version -int 1

Make an AFP connection to another system so that the AFP Client preference file will be filled in with the default set of values. Note: You must connect as a registered user, not as a guest.
Execute the following command to see a list of the disabled User Authentication Methods (UAMs)

defaults read /Library/Preferences/com.apple.AppleShareClient afp_disabled_uams

By default the disabled UAMs are "Cleartxt Passwrd", "MS2.0", "2-Way Randnum exchange", and "DHCAST128". Note: if you don't see a list, restart your computer and repeat step 3.

To enable one of these UAMs, remove it from the list of disabled UAMs. For example, this command enables DHCAST128 by removing it from the list of disabled authentication methods:

sudo defaults write /Library/Preferences/com.apple.AppleShareClient afp_disabled_uams -array "Cleartxt Passwrd" "MS2.0" "2-Way Randnum exchange"
After the desired changes have been made, restore the permissions on the Preferences folder with this command:

sudo chmod o-w /Library/Preferences
Additional Information
If you want to undo the changes described above, you can either delete the /Library/Preferences/com.apple.AppleShareClient file or use the following command to re-disable the default set of older UAMs:

sudo defaults write /Library/Preferences/com.apple.AppleShareClient afp_disabled_uams -array "Cleartxt Passwrd" "MS2.0" "2-Way Randnum exchange" "DHCAST128"

The full article can be found here:  http://support.apple.com/kb/HT4700