Server returned VALIDATION_ERROR with no error message

[mambo_jumbo]

I have been searching the forums but wasnt able to find an answer regarding error response for restdatasource.
I am using Version v8.2p_2012-05-24/LGPL and chrome browser.
the rest servlet responds with corect formated data for the combobox item and paging is working fine but when the validation on server is used I get the "Server returned VALIDATION_ERROR with no error message" message window instead of the red dot near the element like on client side validation.
I set the validator on the datasource:

isc.RestDataSource.create({
    ID:"siteName",
    
    fields:[
		           {name:"siteName",
		            title:"Select name",
//		            optionDataSource:"siteJVID",
		            editorType:"ComboBoxItem", 
		            completeOnTab:true,
		            validateOnChange:true, 				        	
		            validators:[{type:"regexp", expression:"^[a-zA-Z0-9]*$", errorMessage:"wrong charachter"}]
				}
    ],
    dataFormat:"json",
    dataURL:location.href+"ServletForNames",
    operationBindings:[
                       {operationType:"fetch", dataProtocol:"getParams"},
                       {operationType:"add", dataProtocol:"postParams"},
                       {operationType:"remove", dataProtocol:"getParams", requestProperties:{httpMethod:"DELETE"}},
                       {operationType:"update", dataProtocol:"postParams", requestProperties:{httpMethod:"PUT"}}
                     ],

});

on the client side it shows as dot but with the server response it give the error window. The response looks like this:

 {    response:{   status:-4,errors:{  siteName:[{errorMessage:"DB communication error1"},{errorMessage:"DB communication error2"}]}}}

Can someone point to right direction what I am doing wrong?
Thanks