SharePoint Web Services. Using UserPofileService.GetUserProfileByName. After SP upgrade... failing

The below web services code has worked properly for me for over a year. We have updated our SharePoint servers, and now the below code throws an exception (at the bottom line of code) "Object reference not set to an instance of an object"

UserProfile开发者_StackOverflowWS.UserProfileService userProfileService = new UserProfileWS.UserProfileService();

userProfileService.Credentials = System.Net.CredentialCache.DefaultNetworkCredentials;

string serviceloc = "/_vti_bin/UserProfileService.asmx";
userProfileService.Url = _webUrl +  serviceloc;

UserProfileWS.PropertyData[] info = userProfileService.GetUserProfileByName(null);

EDIT: The service is still there. I browse http:///_vti_bin/UserProfileService.asmx, and the information for the service is still there, including the full description of the GetUserProfileByName call.

EDIT2: This does appear to be due to a change in SharePoint. I loaded a previous version of my software (known to be working), and it exhibits the same erroneous behavior.

try

UserProfileWS.PropertyData[] info = userProfileService.GetUserProfileByName(userName);

as specified http://msdn.microsoft.com/en-us/library/microsoft.office.server.userprofiles.userprofileservice.getuserprofilebyname(v=office.12).aspx

When was the farm updated? Was the WSS updates installed before the MOSS updates? If you believe it to be a problem as a result of infrastructure updates, build a test farm and try the code against pre-updates (go back as far as a year ago to start off).