In Photoshop, click Edit|Preferences|Camera Raw
At the bottom of the dialog box, next to TIFF, select Disable TIFF support
If that doesn't fix it and if you are using Windows try this:
Right-click on a TIFF
Select Open with|Choose default propram
Select the desired program
Check Always use the selected program to open this kind of file.
I have a weird problem with PS6. With certain TIFF files, whether I try to open or place, the file opens in Camera Raw (7.4). I've tried every way I think of to thwart this but it's always the same. The same file exists in an image database with Lightroom. Sure, I can just go ahead and have Camera Raw open the file as is, but then it changes the metadata of the file and then Lightroom tries to figure out what to do next time it encounters the file.
Any thoughts on what causes this and how to fix it?