Tungsten T3 & new SD cards

Having had great use from Tom Tom Navigator for T3 I bought POIsoft's postcode program. To get enough space I bought a new SD card and used quick install to get the satnav on it. This is now working fine, however, my PC will only browse the card and tells me the card is locked when I try to copy the POI software onto it. It isn't the physical lock I've tried both positions! So what is it I'm doing wrong?

The problem was an intermittent fault on the card reader! New box solved it.