Customer failed to login to TSIM with any user and got message:invalid user or password in the login page.
Found exceptions in bppmws.log in TSIM server as below:
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WARN  11/20 21:26:05 [Thread-10,RequestExecutor] HttpRequestExecutorTask Connection failure  occurred for  URI [https://xxxxxxxxx:443/tsws/10.0/api/authenticate/login ]
javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
....
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 Mentioned error indicates that HandShake error between TSIM and TSPS which is caused by the missing of TSPS certificate in TSIM server and thus it blocked the authentication request from TSIM to TSPS via web service.

So need to import the private TSPS cert into TSIM server by following steps:
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Login to TSIM and open a command line window
#Microsoft Windows
set PATH=<Infrastructure Management Server Installation Directory>\pw\jre\bin;%PATH%
#Unix
export PATH=<Infrastructure Management Server Installation Directory>/pw/jre/bin:$PATH

For example in Windows:
Set the PATH variable:
set PATH="D:\Program Files\BMC Software\TrueSight\pw\jre\bin";%PATH%
Change directory to “D:\Program Files\BMC Software\TrueSight\pw\pronto\conf”
Import the TSPS server certificate via command:

keytool -import -alias truesightserver -keystore pnserver.ks -file <tpsp server cert>.cer -storetype JKS -storepass get2net

Restart the TSIM Server using command "pw system stop/start"
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As for the detailed of the certificate creation and importing, please refer to:
https://docs.bmc.com/docs/display/TSOMD107/Applying+TrueSight+Presentation+Server+certificate+to+the+TrueSight+Infrastructure+Management
  

Note: From TSIM 11.3.02 onward, The Infrastructure Management Server has a set of pw commands  including a command to  import the certificates, e.g.  pw certificate import TSPS 
Please refer below link for more details.
https://docs.bmc.com/docs/TSOperations/113/creating-and-importing-certificates-in-truesight-infrastructure-management-860483721.html
For TSIM 11.3.04
https://docs.bmc.com/docs/TSOperations/11304/creating-and-importing-certificates-in-truesight-infrastructure-management-937358218.html