When I upgrade to jQuery 1.5.1 (or 1.5) all of the ajax() calls in my site produce a "parserror" in the error option function. There is also a script error 
Uncaught SyntaxError: Unexpected token : jquery-1.5.1.min.js:16
The site has been running w/o errors using 1.4.4. Here is code from one of the ajax() calls.
$.ajax({
  url: '/CustomerGroup/Get',
  type: 'POST',
  contentType: 'application/json; charset=utf-8',
  dataType: 'json',
  success: function (grp) {
    if (grp != null) {
      clear();
      group = grp;
      load(grp);
    } else{
        showError(
                    'Customer Group',
                    'Whoops, error getting customer group information. Please contact support@myorg.com and include your username and date/time of the error.'
                    );
            }
  },
  error: function (x,s,e) {
    showError(
      'Customer Group',
      'Whoops, error getting customer group information. Please contact support@myorg.com and include your username and date/time of the error.'
      );
  }
});
After much research I can not figure out why the error is occurring. Any insights appreciated.
EDITED: With the full version of jQuery I get the following:
Uncaught SyntaxError: Unexpected token :
d.d.extend.globalEvaljquery-1.5.1.js:16
d.ajaxSetup.converters.text scriptjquery-1.5.1.js:16
bJjquery-1.5.1.js:16
wjquery-1.5.1.js:16
d.support.ajax.d.ajaxTransport.send.cjquery-1.5.1.js:16
and YES I am using jquery.validate.
 
     
     
     
    