Check the bits on the SETTING page called "INPUT DEVICE 1" and "INPUT DEVICE 2" INPUT DEVICE 1 should be set to "0" and INPUT DEVICE 2 should be set to "1" for RS232 input of data. If they're both "0", then when you press the READ button, the tape reader will click in and try to read a paper tape. If there's no tape in the reader, nothing will read.
The best way to expand the memory on Fanuc 6T and 6M controls is to add a BTR connection. You can put a PC near the machine, run files directly off the PC in TAPE mode, upload/download files with an RS232 port, access files from a network server (through the PC) and do background editing while the machine is running. For the price of an old PC and a BTR kit, you can add a lot of capability to the Fanuc 6. Larger bubble memory boards are outrageously expensive. For info, see our "MultiPort PC-DNC Editor" with the Fanuc BTR connection at www.rym.com or www.sub-soft.com