Well, I talked to the IBM support team and it helped indeed.
My problem was, that I didn't really understand, how to install the TM1 contributor with TM1 9.5.2, because the official installation manual is slightly cryptic, at least when reading it for the first time
I haven't had the Apache Tomcat installed properly, because I assumed, that the IIS would be sufficient to run the TM1 Contributor, like it is with TM1 Web. That was wrong, since I installed everything on a single machine. One needs first to understand the picture of the architecture in the file "tm1_install.pdf" on page 52. The IIS is only for the TM1 Contributor Web client. The Portal, Workflow and the IBM Cognos Rich Client Framework (Administration) need a Java Web Application Server. This can be an IBM WebSphere or the Apache Tomcat. The IBM support guy recomended installing the Apache Tomcat.
Here are the TM1 Contributor installation steps for dummies on a single machine.
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The (leading) BEFORE install steps:
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(1) Install the Microsoft IIS webserver.
(2) Install the Microsoft .Net Version 3.5 SP1 (or better) Framework.
(3) Install Java: Install the JRE 6.0 Update 12 (or better). I installed the JRE 6 Update 24.
(4) Install a Java based application server. Either Apache Tomcat Version 6.0.18 (or better) or IBM WebSphere Community Edition. I installed the Apache Tomcat 6.0.32 as a core 32-bit/64-bit Windows Service Installer.
(5) Install the TM1 9.5.2 with the TM1 Contributor.
(6) Check, if Apache Tomcat is running:
http://localhost:8080/ should show you the Apache Tomcat page, if you defined the default port as 8080.
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The (trailing) AFTER install steps:
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(1) Preparing Apache Tomcat
(1.1) After installing Tomcat open Windows Services and stop the Apache Tomcat 6 service.
(1.2) In Windows Explorer browse to the Apache install location and open the Conf directory.
(1.3) The default location is: C:\Program Files\Apache Software Foundation\Tomcat 6.0\conf
(1.4) Using a text editor open the tomcat-users.xml file and set the encoding to UTF-8. Save the tomcat-users.xml file.
(1.5) Return to Windows Services and start the Apache Tomcat 6 service.
(2) Open Tomcat Manager and deploy the pmpsvc.war file manually.
(2.1) Open Apache Manager. From the Start menu click Programs > Apache Tomcat 6 > Tomcat Manager.
(2.2) When prompted, enter the credentials supplied when you installed Apache and click OK.
(2.3) In the Tomcat Web Application Manager screen scroll to the Select WAR file to deploy section
(2.4) Click Browse button and go to the <install directory>\Cognos\TM1\Cadmin directory and select the pmpsvc.war file.
(2.5) Click Deploy.
(2.6) This may take a few minutes to complete. Once the process completes scroll to the Applications section and find the pmpsvc app signifying TM1 Contributor.
(3) Configure the pmpsvc
(3.1) Click /pmpsvc. You must then define the location of the Admin Host, Server Name and TM1 Web Client URL. If it is an all-in-one install it will dynamically populate these entries. If a change is needed later on it is still possible from the home page of the IBM Cognos TM1 Contributor Manager (click the Tools button).
(3.2) Click OK after ensuring these entries are correct. The TM1 Server authentication prompt appears.
(3.3.) The IBM Cognos TM1 Contributor Planning Administration site now appears.
From here you can configure the TM1 Contributor using the Contributor Documentation.
Start the TM1 Contributor in the browser generaly with:
http://machine:8080/pmpsvc
http://localhost:8080/pmpsvc