So I uninstalled U10, installed it again with the common "password equals username" as it was in all the U9.6 installations. Cost me some time and leaves me with the question why "the lab" has changed the installation script.

In practice, at most customers' sites security and the password policies do not allow for "password equals username". The Uniface 9 defaults exactly led to the situation you are now describing. By providing a different default for password, we aim to be more compliant with common password policies (at least one uppercase character, at least one digit). Obviously the password provided are mere suggestions that the user is expected to review, accept or change (Setup will create the account using the specified password. Make sure the password is compliant with your password policy). What the installer does is:

1. If the account urouter or userver does not exist: create it in the Uniface Servers group with the password provided. The creation will fail if the password is not compliant with password policies
2. If the account urouter of userver exists already (form a previous installation): validate that the account can login using the password provided. The installer will fail if the password is not valid.

The problem you are running into is three-fold:

1. The moment that the creation/password check of an existing urouter /userver account is validated should take place before the installation actually starts, enabling you to make changes before you run into the perceived error. This is due to a limitation on the Installer Program
2. The feedback if an error has occurred as described above could provide a better explanation. Here we are confronted with limitations in our implementation of Install Shield, which does not allow more than a few lines of feedback text.
3. Actually there is no need to uninstall/reinstall: the users already existed on your machine and could not be created or reused with the password provided. In fact, all you need to manually change is the password specified for the userver account in {install dir}\\uniface\\webapps\\uniface\\WEB-INF\\web.xml. 

Longer term we are looking into a new Installation Utility, providing a better User Experience, that addresses points 1 and 2 and makes the corrective action in point 3 redundant. Henk van der Veer Program Manager Uniface 10

on your: The Uniface 9 defaults exactly led to the situation you are now describing. I see it more: the changed defaults led to that situation; In my 2nd installation I just used these "old" passwords without any problem at all.   But now to the more important issues:   Your 3. fixes the userver password with a small change in the referenced file, perhaps in the error message, there should be room for the: adjust {install dir}\\uniface\\webapps\\uniface\\WEB-INF\\web.xml.    But where and how fixing the urouter password problem?

on your: The Uniface 9 defaults exactly led to the situation you are now describing. I see it more: the changed defaults led to that situation; In my 2nd installation I just used these “old” passwords without any problem at all.

That is probably because you don't have a strong password policy on your computer. If the user account urouter does not exist yet but the installer is not able to create that user due to a password policy requirements , you will see the following error:

An error has occurred while creating the user account for urouter: Group <UNIFACE Server Users> already exists. The username and/or password does not meet all password policy requirements.

The urouter password is not stored in any Uniface configuration file. If a the user account urouter has been created by a previous Uniface installation and the user performing a subsequent installation specifies a different password, the installer will report that:

An error has occurred while creating the user account for urouter: Group <UNIFACE Server Users> already exists. User <urouter> already exists, password is incorrect.

Considering the urouter there is no need for action: the newly installed urouter server process will happily be started using the already existing local urouter account on your Windows PC. 

I was quite happy and installed all swinuf96... up to the latest one on my test PC using the defaults.   Think we can agree that the conflict would not have occured if not only the default for the password, but the default for the linked username would have been modified as well.