I had a client that installed the web client on a IIS 6 web server and everything seemed fine.  When he tried to login, he received the error: Keyword not supported: 'iuser id'.  For the life of me, I was unable to figure out what was causing this issue.  I looked in the Rightfax Remoting services and verified that the proper username and password was entered correctly.  Everything seemed right, but it was not.

Here is an example of the string that the Remoting service was using:

data source=SERVER\RightFax;password=PASSWORD;iuser id=sa;initial catalog=RightFax

Here is an example of a WORKING Remoting service string:

data source=SERVER\RightFax;password=PASSWORD;user id=sa;initial catalog=RightFax

Now, when looking at this, everything looks identical and correct.  When looking closer, the non-working string has iuser instead of user.  Once I changed the username to user, everything worked without a hitch!