A popular question on many forums goes something like this "Outlook isn't recognized by [application_name]. The error is that Outlook isn't my default mail program, but when I check the Default Programs, Microsoft Outlook is the default for everything."

First and foremost, when you receive this message with Outlook 2010 64-bit, try the 32-bit version of Office. Few applications work with the 64-bit version and unless you need to open large (2 GB) Excel and Access files, you should not use the 64-bit version. Wanting to use the 64-bit version because you use a 64-bit operating system isn't enough reason to use it - stick with the 32-bit build this time around.

Repeat: Avoid the 64-bit version unless you have confirmed the add-ins and utilities you want to use will work with it. There is no benefit to using the 64-bit version for typical users - Office is not going to run faster or better. Only those who work with huge (2GB) record sets and spreadsheets need the 64-bit version. The 32-bit version works fine on 64-bit Windows (do not use compatibility mode).

While many applications will work with the 32-bit version of Outlook, some programs will need to be updated before they will work with Outlook 2010 32-bit. Included on this list is Blackberry's Desktop Manager and Quicken 2010. If you need these programs, you will need to stick with an older version of Office for now.

Note: If you are using a Click to Run suite, add-ins will not work with it.

If you sync with a smartphone or pda, you need to confirm your device will sync with the 64-bit version of Outlook. At this point in time, most sync software does not work with the 64-bit version (or Outlook 2010 32-bit for that matter). A short list of add-ins will work with it, but many more only work with the 32-bit version of Outlook.

From Microsoft: "Office 2010 provides support for the 32-bit version of Office 2010 programs running on 64-bit operating systems by using WOW64, a compatibility environment provided by the operating system that allows a 32-bit application to run on a Windows 64-bit operating system. Using the 32-bit version of Office 2010 allows people to continue to use existing third-party add-ins for Office that are 32-bit. The 32-bit version of Office 2010 is the recommended option for most users, because it prevents potential compatibility issues with other 32-bit applications, specifically third-party add-ins that are available only for 32-bit operating systems."