Don’t seem to play nice.
It seems that both call create a function called … Number.function and error out when used together.
Error:
[Exception... "'Sys.ParameterCountException: Sys.ParameterCountException: Parameter count mismatch.' when calling method: [nsIDOMEventListener::handleEvent]" nsresult: "0x8057001c (NS_ERROR_XPC_JS_THREW_JS_OBJECT)" location: "<unknown>" data: no]
Solution:
Don’t use ASP.NET AJAX if your using the vastly superior Dojo Toolkit 
I submitted a bug to dojo but it looks like it won’t be fixed unless there is a test harness. I understand…who even runs ASP.NET AJAX
Anyone have a server we can host a test on?
[...] http://eric.polerecky.com/archives/dijitformvalidationtextbox-and-aspnet-ajax/ [...]
I am facing same issue with my application. Did you find any solution?
I have not. I'm surprised its not a bigger issue.