Excel Services trying to use port 80 for a web app on a different port.

We have numerous web applications installed and they were all working well with Excel Services.

We had to change the default port 80 to accept anonymous, this seems to have stopped our Excel web services working properly.

We have an app on port 23888 that users open a excel file in the browser with Excel (office web apps), this used to open perfectly, users can make changes and close the file.

Since we had to make port 80 include anonymous authentication the users get "you do not have permissions to open this file".

Looking at the log files, the file tries ot use the xlviewer via port 80 and not 23888

http://servername:80/_layouts/xlviewer.aspx?id=filenamegoeshere

We also use "Alternate Access mappings" on this app, if we use the default url with the port 23888 it works perfectly. If we use the AAM it goes to port 80.

Any ideas as to why it is doing this?