Ah, perhaps a mod conflict. What mods are you running?
On screenshots, I've found the simplest way (for me) is to hit Print Screen. That saves a .tga file to your C:\Users\Browd\Documents\My Games\Sid Meier's Civilization 5\ScreenShots folder. Use your favorite image editor (I prefer a freeware program, IrfanView) to do any editing you want to do (crop image, circle things you want to emphasize, etc.) and then "Save As" a .jpg or .png file that you can upload as an attachment to your message (or post to a third-party site, like ImageShack, and link to your message).
Alternatively, you can upload a save file, but if you are running mods, not everyone will be able to open it.