I can try to help you if you can provide me some more info:
1.What is the current version of Reader in your machine?
2.How exactly are you trying to update it to 9.3.4?
My current version of Reader is 9.3.3 and I'm trying to update it from an automatic update icon located in the lower right-hand corner tray. Thank you for trying to helpme.
Your current installation may be corrupted somehow. Try to uninstall it from Add/Remove Programs.
If the normal uninstall also fails, use the Windows Installer Cleanup Utility to remove your current version, then install it again from scratch. The utility is no longer available from Microsoft, but you can download it from http://majorgeeks.com/Windows_Installer_CleanUp_Utility_d4459.html - ask, if you need instructions how to use it.
Just adding to what ʇɐb ɹəuəllıʍ has said above,after cleaning the corrupt installation :
•download the 9.3.3 installer http://ardownload.adobe.com/pub/adobe/reader/win/9.x/9.3.3/enu/AdbeRdr933_en_US.exe and run it;
•download the 9.3.4 update http://ardownload.adobe.com/pub/adobe/reader/win/9.x/9.3.4/misc/AdbeRdrUpd934_all_incr.msp and run it.
Hooray! Your advise worked perfectly! Thank you very much! I had tried Add/Remove Programs before and it had failed. The Windows Installer Cleanup Utility solved the problem.
Hooray! Both your advise solved the problem. Thank you very much. I had tried the Add/Remove program but it failed. The Windows Installer Cleaner Utility seems to be an important tool.