Almost every time the schema browser is open (Vista machine), this error occurs. The initial display is fine, then click once to select a table and a dialog box appears, "The application has encountered a problem. We are sorry for the inconvenience."
After clicking OK, another prompt appears, "[SafeCall Exception]: The system can't find the path specified" (or Access denied). Occasionally, but rarely, the schema browser performs as normal. Sometime normal work can continue after these errors. More often, Toad needs to be restarted.
Conflict accessing the SBHist.xml file.
View | Options | Schema Browser | Left Hand side and uncheck "restore history on connection" and set the limit down to 1.
In Toad 10.5 and older, setting this will reduce the occurance of the error, but it will still occur when exiting Toad. A user should still be able to exit after clicking OK to this prompt.
This issue has been fixed in Toad for Oracle 10.6. You can download this version at https://support.quest.com/SUPPORT/index?page=downloads.