Did SACL provide any reason for not renewing the contract? Did they mention anything at all about "security" being of concern?
I don't think you can blame the Office of Transport Security for this as nothing in the regs precludes persons visiting airside provided the VIC requirements are complied with. All that is required is for the person/s to have lawful reason for being airside. Lawful reason is not defined anywhere.
ps. DOTARS is dead - has been since KRudd came to power.