IAX and AES encryption

Dear all,
I have 1 major asterisk server (Server A) and two satellites (B and C respectively). A and B are interconnected via IAX without any problems. Both servers are FreePBX distros and were set up with the help of GUI. Server C runs manually compiled Asterisk 13. Yesterday I tried to connect it to Server A via IAX and it was successfull, except when I a call from Server C goes to Server A I observer the following:

Server C

> [Jun 21 14:07:01] WARNING[3979]: chan_iax2.c:1215 iax_error_output: Invalid information element contents, strange boundary
> [Jun 21 14:07:01] WARNING[3979]: chan_iax2.c:10202 socket_process_helper: Undecodable frame received from 'xx.xx.xx.xx:4569'
> [Jun 21 14:07:01] WARNING[3972]: chan_iax2.c:1215 iax_error_output: Invalid information element contents, strange boundary
> [Jun 21 14:07:01] WARNING[3972]: chan_iax2.c:10202 socket_process_helper: Undecodable frame received from 'xx.xx.xx.xx:4569'
> [Jun 21 14:20:47] NOTICE[3979]: chan_iax2.c:10166 socket_process_helper: Packet Decrypt Failed!
> [Jun 21 14:20:48] NOTICE[3978]: chan_iax2.c:10166 socket_process_helper: Packet Decrypt Failed!
> [Jun 21 14:20:49] NOTICE[3977]: chan_iax2.c:10166 socket_process_helper: Packet Decrypt Failed!

Server A

> [2017-06-21 14:07:08] WARNING[1562]: /usr/src/jessie/asterisk13-13.15.0/include/asterisk/crypto.h:179 __stub__ast_aes_decrypt: AES encryption disabled. Install OpenSSL.
> [2017-06-21 14:07:08] WARNING[1562]: /usr/src/jessie/asterisk13-13.15.0/include/asterisk/crypto.h:179 __stub__ast_aes_decrypt: AES encryption disabled. Install OpenSSL.
> [2017-06-21 14:07:08] WARNING[1562]: chan_iax2.c:1215 iax_error_output: Invalid information element contents, strange boundary
> [2017-06-21 14:07:08] WARNING[1562]: chan_iax2.c:10202 socket_process_helper: Undecodable frame received from 'yy.yy.yy.yy:4569'

OpenSSL is installed on Server C.

> osmc*CLI> module show like res_crypto
> Module                         Description                              Use Count  Status      Support Level
> res_crypto.so                  Cryptographic Digital Signatures         1          Running              core
> 1 modules loaded
> osmc*CLI> module show like res_timing_pthread
> Module                         Description                              Use Count  Status      Support Level
> res_timing_pthread.so          pthread Timing Interface                 0          Running          extended
> 1 modules loaded

Any help/advice is highly appreciated.

Thank you.
With regards, Evgenii.