Most common:
A: Bad comm port number selection. If the radio reacts to the 'Clone Read' command, this probably isn't the problem, unless...
A(1) Set the comm port settings to defaut and try reading the radio. 9800/8/N/1 with default fast FIFO buffers should be correct. "They" may have changed the settings while programming a different radio. Also, newer computers and OS' don't always get along with DB9 or DB25 serial communications, and all USB to RS232 converters are not equal. Check device manager for comm port conflicts. The genuine Icom USB OPC1122/U cable is very reliable as long as the "helpful" computer didn't automatically change the comm port on you.
Other possibilities:
B: "They" programmed the radio with a higher software version. CS-F500 2.3 is the latest. Older SW versions won't read newer version programmed radios.
C: Common | Common | Security | Transceiver Data Out was changed to inhibited on the last upload. The radio may be over-written, but CANNOT read.
Less Likely:
D: Dirt or goo in the microphone port. BE CAREFUL using solvents!!
E: Damaged programming cable. Check the comm port settings and try reading another radio.
F: "They" spilled Diet Mountain Dew into the radio and it corroded the front panel and/or main board and/or ribbon cable. "They" will never fess up to the accidental spill. That will get progressivly more ugly later. (Been there.)
My most common error after (A) wrong comm port:
G: You are using the 3.5MM to RJ45 adapter connected to nothing, or to a 3.5MM OPC478. Either way it won't work. After ten years as an Icom dealer, I still catch myself trying to do that. Duuh.
Best of luck!