All UDT API will return an error upon a failed operation. Particularly, UDT defines UDT::INVALID_SOCK and UDT::ERROR as error returned values. (several routines return false as error value.) Application should check the return value against these two constants.
| Error Name | Error Code | Comment |
| SUCCESS | 0 | success operation. |
| ECONNSETUP | 1000 | connection setup failure. |
| ENOSERVER | 1001 | server does not exist. |
| ECONNREJ | 1002 | connection request was rejected by server. |
| ESOCKFAIL | 1003 | could not create/configure UDP socket. |
| ESECFAIL | 1004 | connection request was aborted due to security reasons. |
| ECONNFAIL | 2000 | connection failure. |
| ECONNLOST | 2001 | connection was broken. |
| ENOCONN | 2002 | connection does not exist. |
| ERESOURCE | 3000 | system resource failure. |
| ETHREAD | 3001 | could not create new thread. |
| ENOBUF | 3002 | no memory space. |
| EFILE | 4000 | file access error. |
| EINVRDOFF | 4001 | invalid read offset. |
| ERDPERM | 4002 | no read permission. |
| EINVWROFF | 4003 | invalid write offset. |
| EWRPERM | 4004 | no write permission. |
| EINVOP | 5000 | operation not supported. |
| EBOUNDSOCK | 5001 | cannot execute the operation on a bound socket. |
| ECONNSOCK | 5002 | cannot execute the operation on a connected socket. |
| EINVPARAM | 5003 | bad parameters. |
| EINVSOCK | 5004 | invalid UDT socket. |
| EUNBOUNDSOCK | 5005 | cannot listen on unbound socket. |
| ENOLISTEN | 5006 | (accept) socket is not in listening state. |
| ERDVNOSERV | 5007 | rendezvous connection process does not allow listen and accept call. |
| ERDVUNBOUND | 5008 | rendezvous connection setup is enabled but bind has not been called before connect. |
| ESTREAMILL | 5009 | operation not supported in SOCK_STREAM mode. |
| EDGRAMILL | 5010 | operation not supported in SOCK_DGRAM mode. |
| EDUPLISTEN | 5011 | another socket is already listening on the same UDP port. |
| ELARGEMSG | 5012 | message is too large to be hold in the sending buffer. |
| EASYNCFAIL | 6000 | non-blocking call failure. |
| EASYNCSND | 6001 | no buffer available for sending. |
| EASYNCRCV | 6002 | no data available for read. |
| ETIMEOUT | 6003 | timeout before operation completes. |
| EPEERERR | 7000 | Error has happened at the peer side. |