Can you create a test page? Or some code to duplicate the problem.
In this case I'm sure I can find the reason.
from your code it comes that the error is raised from the following function (decompressed):
function fn_Node_GetProperty(ch_node, ch_propertyName)
return ch_node[ch_propertyName] == null && ch_node.pt_nodeType && typeof(ch_node.pt_nodeType[ch_propertyName]) != 'undefined' ? ch_node.pt_nodeType[ch_propertyName] : ch_node[ch_propertyName];
Where ch_node is your node, and ch_propertyName is "NavigateUrl" (which is _4N when compressed).
Anyway I don't think this will help.
The only way is to reproduce the error in a test case.
Thanks and sorry for inconvenience.