SCP training input error message in semi-automatic classification

I have been doing some land classifications and everything was working fine, until it wasn’t. I keep getting the same error message when I try to calculate the signatures from the ROI creation:

[Information 3]: Select SCP training input; input not loaded

I do get a warning earlier when I try create a bandset, not sure if it is related:
[Warning 13] Unable to load the virtual raster. Please create it manually

I am working on a MAC Sierra, and I have tried uninstalling the plugins and the program (QGIS 2.18) neither of which worked.

I cannot create any relevant tags…