Apple consistently tightens up its quarantine provisions (what they call 'Gatekeeper') in order to stop malicious software from being downloaded and installed on a Mac.  if you can't open your BookingCenter Desktop Mac OS X download, because of an error (usually an .icon file) then it is usually the case your download has been 'quarantined'.  Here is how you can fix it.

Open Terminal, the app found in your Applications | Utilities folder that ships with all versions of Mac OS.

Run the following 2 commands using terminal (we recommend copying/pasting from below):

1.   cd /Applications/BookingCenter

--> this puts your Terminal session inside the BookingCenter folder, whihc shoudl be installed in your /Applications/ folder.

  2.  xattr -r -d com.apple.quarantine BookingCenter.app/

--> This command edits the 'quarantine' from the files inside the BookingCenter folder.

After you have done these 2 commands, the BookingCenter Desktop aplication should open without issues.  If you cannot use Terminal due to your access level restrictions on the Mac OS X you are using, then get an administrator to assist with the 2 commands above for you.