Not up on my Mac OS numbers -- is that part of the kitty-cat series (Panther, Leopard, etc.) or the national park series (Yosemite, El Capitan, etc.)?
Do you have more than one AE version on this machine?
And if this OS really is only a year or two old, It's a wonder you got CS5 to run on it at all.
Hi Dave. It's Leopard I believe.
Did AE CS5 EVER work well for you? Is this something new?
I presume you've taken the normal remedies: fixed OS permissions, restarts, trash AE Preferences, etc.
I've done multiple restarts. Permissions seem fine. Haven't trashed AE Prefs tho... will try that. The program was running fine for a couple of years and then... this started. Haven't been able to use it since.
Can't get in to trash the Prefs... can't open the program... is there another way?
What is the exact error message? Screen shot is easiest.
If it's complaining about multiple versions of a plug-in, you'll need to track down the duplicates. (In later versions of AE it gives you more helpful information in the error message, but CS5 is what it is. Or was.)
For CS5 on a Mac, the standard locations for plug-ins are:
/Applications/Adobe After Effects CS5/Plug-ins
Be sure to check any sub-folders you find in those folders.