When you launch the Activesync 4.1 setup you may get the following error:

Command line parameters:
/L language ID
/S Hide initialization dialog. For silent mode use: /S/v/qn.
/V parameters to MsiExec.exe
/UA
/UW
/UM

This happens due to missing or incorrect TEMP or TMP environment variables. When you download setup.msi from Microsoft, the setup will first extract all the files to your Windows XP Profile’s Temporary folder (%temp% , not c:\windows\temp)

To resolve this error:

Go to your System Properties—->Advanced—->Environment Variables

Make sure you have the following user variables:

1) TEMP- %USERPROFILE%\Local Settings\Temp
2) TMP- %USERPROFILE%\Local Settings\Temp

If you don’t, manually add these variables. After adding these variables, restart the computer and try to launch the setup and it should run normally.