automate Flash Player 21.0.0.213 installation

We are trying to install latest Flash Player 21.0.0.213 automatically on several Windows 7 64-Bit systems (mostly German  some English). We are having difficulties to upgrade especially from older versions and install Flash Player 21.0.0.213 afterwards. I have to admit every single Flash Player version update is my personal administrative nightmare.

We are calling latest Flash Player uninstaller before we install Flash Player 21. We tried to install via msi and exe, without a difference. The result after we assign the package to the system is that older versions of Flash Player are removed but Flash Player 21 is not installed. If I assign the same package again it finally installs it successfully. We even tried to change to install twice in our scripts -  no solution, same behaviour.

Is there a documentation available what is failing here ? We have a C:\Windows\SysWOW64\Macromed\Flash\FlashInstall.log available but couldn't find a source that documents how to interpret the contents of this file:

=O====== M/21.0.0.213 2016-04-19+09-27-56.000 ========

0000 00000010 C:\Windows\TEMP\1461053786.OCS\data\install_flash_player_21_active_x.exe -install

0001 00001036 Software\Macromedia\FlashPlayerActiveX/PlayerPath 2

0002 00001036 Software\Macromedia\FlashPlayer\SafeVersions/21.0 2

0003 00000011 1

0004 00000020 C:\Windows\SysWOW64\FlashPlayerCPLApp.cpl

0005 00001037 SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Adobe Flash Player ActiveX/ 2

0006 00001037 SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\\FlashUtil32_21_0_0_213_ActiveX.exe/ 2

0007 00000013

0008 00000015 C:\Windows\SysWOW64\Macromed\Flash\FlashUtil32_21_0_0_213_ActiveX.exe

0009 00000016 C:\Windows\SysWOW64\Macromed\Flash\FlashUtil32_21_0_0_213_ActiveX.dll

0010 00000023 C:\Windows\SysWOW64\Macromed\Flash\activex.vch

0011 00000019 C:\Windows\SysWOW64\FlashPlayerCPLApp.cpl

0012 00001031 C:\Windows\SysWOW64\FlashPlayerCPLApp.cpl:5

=X====== M/21.0.0.213 2016-04-19+09-28-01.709 ========

=O====== M/21.0.0.213 2016-04-19+09-28-01.803 ========

0000 00000010 C:\Windows\TEMP\1461053786.OCS\data\install_flash_player_21_plugin.exe -install

0001 00001036 Software\Macromedia\FlashPlayerPlugin/PlayerPath 2

0002 00001036 Software\Macromedia\FlashPlayerPlugin/Version 2

0003 00000011 1

0004 00000020 C:\Windows\SysWOW64\FlashPlayerCPLApp.cpl

0005 00001037 SOFTWARE\MozillaPlugins\@adobe.com/FlashPlayer/ 2

0006 00001037 SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Adobe Flash Player NPAPI/ 2

0007 00001037 SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\Adobe Flash Player Plugin/ 2

0008 00001036 Software\Mozilla\Firefox\extensions/Plugins 2

0009 00001036 Software\Mozilla\Mozilla Firefox\extensions/Plugins 2

0010 00001036 Software\Opera Software/Last CommandLine 2

0011 00001036 Software\Opera Software/Last CommandLine 2

0012 00001036 Software\Opera Software/Plugin Path 2

0013 00001036 Software\Opera Software/Plugin Path 2

0014 00001037 SOFTWARE\Microsoft\Windows NT\CurrentVersion\Image File Execution Options\\FlashUtil32_21_0_0_213_Plugin.exe/ 2

0015 00000014

0016 00000015 C:\Windows\SysWOW64\Macromed\Flash\FlashUtil32_21_0_0_213_Plugin.exe

0017 00000024 C:\Windows\SysWOW64\Macromed\Flash\plugin.vch

0018 00000017 C:\Windows\SysWOW64\Macromed\Flash

0019 00000022 C:\Windows\SysWOW64\Macromed\Flash\FlashPlayerPlugin_21_0_0_213.exe

0020 00000019 C:\Windows\SysWOW64\FlashPlayerCPLApp.cpl

0021 00001031 C:\Windows\SysWOW64\FlashPlayerCPLApp.cpl:5

=X====== M/21.0.0.213 2016-04-19+09-28-07.044 ========