I don't see any errors in the library.
Try to send wrong packets log to SMSC technician.
Possible they can analyze it and tell you the reason.

It is written in v3.4 specification

9th symbol is always null (0x00)


C-Octet String
A series of ASCII characters terminated with the NULL character.

Does SMSC always send this error code when you send message in UCS2 encoding?

I think you need to ask SMSC side why they return this status for correct messages. Sometimes, because of network buffer size, SubmitSm packet can be received from network using two read operations. Possible SMSC does not wait when they receive second part of SubmitSm packet and it returns ESME_RINV...

SmppClient events should be initialized right after
client = new SmppClient();

client.evDeliverSmComplete += new ALT.SMS.SmppClient.DeliverSmEventHandler(client_evDeliverSmComplete);

Also in your last code you need to rename method client_evDeliverSm to
client_evDeliverSmComplete

Oh, sorry, I did it in wrong project

correct code should start with

client.evDeliverSmComplete += new ALT.SMS.SmppClient.DeliverSmEventHandler(client_evDeliverSmComplete);

client.evDeliverSmComplete += new ALT.SMS.SmppClient.DeliverSmEventHandler(client_evDeliverSmComplete); ... public void client_evDeliverSmComplete(object sender, DeliverSm data) { if (data.SegmentNumber > 0) { AddMessageSegmentToCollector(data); string messageText = SmppClient.GetMessageText(data.Us...

evDeliverSmComplete is event, but you are trying to use it as method

in your code should be line with

client.evDeliverSm += ...

replace it with

client.evDeliverSmComplete += ...

SmppClientDemo application created for connection with only one SMSC.

You need to write your own application. Where you need to make connection and binding with several SMSC, attach each client to required events.
Also you need to reestablish connection when one of the client disconnects.

Try another event evDeliverSmComplete.

In the evDeliverSm event response DeliverSmResp is not sent yet and SMSC waits when client send response.
evDeliverSmComplete event is raised when response already sent.

You need to create several SmppClient instances and connect each to different SMSC.

Your submit_sm messages are ok.
Do you get ESME_RINVMSGLEN when you send short text?

Please try to find out if SMSC supports concatenated messages?
And try SubmitMode.Payload mode.

Do you always have this response?
It looks like server drops connection when you send SMPP packet.
Please check your connection parameters.

Please ask if SMSC defined restrictions for your ID.
Sometimes they are not allow to bind in Transceiver mode.
Or they allow to bind only one connection.