Hi! I purchased GSM Shield (TEL0051 manufactured by DF Robot sold by Jameco Electronics, CA). I can successfully upload sketches to Uno when the GSM Shield is not connected. However, on connecting the GSM Shield I cannot upload sketches. Attached please see error message. Please help!
I had the same issue earlier with my shield. I solved it with changing the RX\TX jumper on the Gsm shield. Maybe you also have it on your type of gsm shield.
If the shield (any shield) is configured to use D0 & D1 for communicating with the Arduino then you will have problems when it is connected as the ATMega328 is programmed using these pins and the shield interferes with this process.