I think Picasa only comes in a 32-bit version, which will work equally fine in Windows 32 or 64 bit. But to send from Picasa through TB, TB must be 32-bit, which also works equally fine in Windows 32 or 64 bit.

If you have TB 64-bit (see Help/About TB), uninstall it, then download the 32-bit installer:

https://www.thunderbird.net/en-US/thunderbird/all/

The profile folder with all your data is separate and not affected.

Hello sfhowes,

It solved the issue with Windows 10! Thank you!