In newly installed LR4, I tried to export Canon CR2 file to jpg but I’m getting following warning - Unable to Export: An internal error has occurred: Win32 API error 2 ("The system cannot find the file specified.") when calling ShellExecuteExW from AgWorkspace.shellExecute. I didn't have any problem with exporting in LR3.
I found answer - "It probably means that the "Post Processing" field at the bottom of the Export panel is blank (default should be 'Do Nothing'). This has cropped up a few times since the LR4 beta started. Simply enter a valid option and the error should disappear." by Jim01403 and it did work. Thanks!