Sounds like you either had bad disc images or they are not in the correct format to start with for PSX2PSP v1.4

PSX2PSP though just reads the ID from the header of the disc image but if the image is not a raw format such as img or bin or even iso (iso for data only track games) the PSX2PSP can't read the header that has this info because it is not located in the correct area of the disc image because of customized code/header info for that format and would fail on a convert even if you put the correct info in manually

multi bin images would fail at a guess unless you do the usual convert to a single bin+cue (never thought to try that to be honest)

Popstation GUI last time I used it (I admit that was years ago) fails on too many games