My code is similar to the PPP example in the documents. The serial port is initialized in InitSimCard().
In the example handshaking is None.
To test in my code in the InitSimCard I set handshaking to None and in TestPPP() set the handshaking to RequestToSend and the original error went away. However, I started getting more errors in other areas where I check for signal strength. (Every few minutes I close PPP and check signal strength, then reconnect to PPP. There are timeout errors now in the signal check code.) It is more stable if I set the handshaking in InitSimCard() and leave handshaking none in TestPPP().
I think I have resolved the error. In a few places where pin addresses get specified I still had some SC20260 instead of SC20100. I think when I started this project the SC20100 wasn’t part of the firmware yet. Anyway I search my entire project for SC20260 and changed everything to SC20100.
Well, ignore the above. I had rolled back to 2.1.0.6000 to test something else, when I updated to 2.1.0.6500 I got the error again.
More testing to follow. . .