Issue between FTP Transmissions | Thales IoT Developer Community

I am having issues between FTP transmissions, mixture of fput, put transmissions.

Before the fault I notice I get a URC ‘Data Connection already open’ message.

It appears as though even a AT^SISC= 1 ‘Internet Connection Close command’ is issued between the FTP transmissions, and appears to accept the command, and therefore I would have expected the connection to close and allow me to establish a new connection immediatedly.

What can cause the connection not be closed after a at^sisc command?

If I inserted a big delay between the FTP transmissions it will complete ok – presumably after some other timeout delay. 

Any thoughts on curing this issue would be appreciated.

I would have included more code, but the Spam filter is stopping me . 

^SIS: 1,0,2100,"S:125 Data connection already open; Transfer starting."

^SISS detected.

SISW: 1,1 detected, ready to accept data

ftpStrLength4 = 174

FTP: Write String Request: AT^SISW=1,174

^SISW: 1,174,0

Uncaught exception: java.lang.NullPointerException:   0

                at aL.a(), bci=30

                at au.run(), bci=260

Senario2:

URC’s as above until 'DataConnection Open'.

 ^SISS detected.

URC - ATEvent

^SIS: 1,0,2100,"S:125 Data connection already open; Transfer starting."

 ^SISS detected.

Service State, SISI:AT^SISI=1

 ^SISI: 1,4,0,0,0,0                                                 … indicating the FTP connection is up and running.

 Repeating the above.

 Bobg