you have probably removed those functions from dude. Either add those
functions back (you can get them from fresh dude installation) or modify your
link appearance not to try evaluating those functions.
In the control panel on the left side of DUDE, look for the Function entry (should be below MIB nodes). Open functions and scroll down and see if snmp_wireless_link_info() is still there. As Uldis said, if its missing, you can reload DUDE. Otherwise, you can rightclick on the link, click on appearance, and delete snmp_wireless_link_info() from the link appearance.
Also added the missing function snmp_wireless_link_info() which has me stumped as to where it went in the first place!
Fortunateley it was not necessary to reload dude (have over 300 devices being monitored!), just installed it on another PC and copied the missing functions over…