Hi Virginia! The error 15 message that you are receiving is probably because your data has been corrupted in some way. If you have a recent backup, you could restore the most recent one. Chances are (since you said you were clicking on an image), that one of the images is corrupt. If you can get into your program okay, try using the utility options (utility/program/check-repair) and/or the fixme.bat. Sometimes they can repair items that we wouldn't think it would, and it's a good practice to use these utilities now and then, anyway.
As for TMG ... I understand that if a person has NEVER used UFT it is easier to learn. But, as with all computer programs, there is always a learning curve. If you are in the area of a users group, I would highly suggest your joining a group and attending the meetings. You can learn lots of tips and tricks that way. If not, I would highly suggest that you peruse the TMG forum boards and learn what you can.
There are some things you can do prior to using TMG that can help in your changeover. If you go to our RUG of Portland site (http://rug1.tripod.com), there are some links that may help you.