Old lexar card reader will not mount

I have an old digital camera and an old Lexar card reader which used to work fine with my old imac! This moring i tried to connect the reader (GS-UFD/20SA-TP) to my computer to get the images off the memery card and when I connected it it didn't show up on my computer - it is working as the light comes on when i connect it.

First stop was a trawl through the lexar site where I found a driver, this turned out to be a windows driver so I emailed lexar and they sent me the mac driver. I installed this, but when I restart my computer is says 'the system extension ..... was installed improperly etc.' I have tried uninstalling it and installing it again but the same thing happens.

I have emailed lexar to see if there is a more recent version but in the meantime I wondered if any of you mac experts have any suggestions...

thank you
Nicki

PS I know that a new compatible card reader is probably cheap as chips but I'm trying to cut down on my landfill contribution!