Hi there,
Remember that OCIO is a framework that is supposed to be installed centrally or in synch with the workflow provided, and OCIO is updated occasionally. This means OCIO, old or newer, is perhaps not the same as the installed one! It can't find the one defined in the file if a different version was used than the installed one.
Please always check the outcome. Typically, the use of ACES causes trouble if the RRT/ODT function is not understood for low dynamic/gamut outputs like REEC 709 or sRGB, which will show up especially with artifacts in 8bit/channel. Typically, the use is connected to wishful thinking about the filmic outcome, which changes if used for higher dynamic and larger Gamuts. Tone mapping or gamut compression is unnecessary, and the "filmic" effect [sic] is gone.
Setting the OCIO to your installation might not create the outcome envisioned by the external creator of the file.
Please check with support if you have a problem with a file created in your unchanged setup.
Cheers