Playback and impulse responses

[megapixel]

I have hit a problem when trying to load any of the Acousticas Bricasti M7 impulse responses into ReaVerb. These are all 48 khz WAV stereo interleaved files. For some reason, having any of these impulses loaded prevents playback of the project, and the only way of unlocking it is to reload Reaper. I don't have a problem running the impulses that are provided with Reaper (like Sweetverbo which is actually rather good). Running in zero latency mode appears to make no difference.

Using MacBookPro with built in soundcard for this.

Any thoughts would be appreciated.