I really don't remember when it happened, but for the last week I have not been able to right click on a file and select "Send To" --> "Mail Recipient." My work computer runs Windows XP SP3 and I use Mozilla's Thunderbird as my email client.

I did find a good thread describing this problem, but none of the workaround seem to work for me.

Mozilla team has this issue as a known bug.  It seems to be related to running the Thunderbird update as opposed to reinstalling a new version.  Another link can be found here describing this problem.

- Chris

Update:

To fix this problem on my machine, I had to change a registry setting.  In one of the links above, they state: "to make a registry setting a path to:"

"C:\Program Files\Mozilla Thunderbird\mozMapi32_InUse.dll

which did not work for me because I did not have a file labeled mozMapi32_InUse.dll on my computer, but I did have one labled "mozMapi32.dll".  So I modified this registry setting use the DLL installed on my computer.  Send To now works for me.

Windows Registry Workaround

This is a better workaround, it will work if you installed Thunderbird with
default settings and you use a English Windows version. Just save the file to
disk and then execute it. If you prefer to apply the workaround manually, you
have to set in the registry HKEY_LOCAL_MACHINE\SOFTWARE\Clients\Mail\Mozilla
Thunderbird the DLLPath key to "C:\Program Files\Mozilla
Thunderbird\mozMapi32_InUse.dll" (without the quotes).
Another workaround is to set another mail client as default mail client (for
example Outlook Express) and then Thunderbird as default mail client again. But
I would not recommend this as this might cause the same problems as in Bug 452162 again.

--Chris