You may see these error codes in log messages for any probe, as well as the hub/robot logs.
Examples:
Jan 4 16:41:41:530 [2476] hub: mkgetqforpostroute - subscribe to nas@/domain/example.dev.domain/example/hub failed 3(invalid argument)
Jan 22 12:07:35:387 [Thread-0, EventLogging] (6) permission denied, Received status (6) on response (for sendRcv) for cmd = 'transaction_list'
May 6 01:03:40:741 [8944] rsp: dbGetAlarmState: ndbExecute exec error(7): temporarily out of resources
Occasionally the error message won't be given, just a code, and you can use the following list to help determine what the underlying error is:
0 ---OK
1 ---general error
2 ---communication error
3 ---invalid argument
4 ---not found
5 ---already defined
6 ---permission denied
7 ---temporarily out of resources
8 ---out of resources
9 ---no space left
10 ---broken connection
11 ---command not found
12 ---login failed
13 ---SID expired
14 ---illegal MAC
15 ---illegal SID
16 ---Session id for hub is invalid
17 ---Expired
18 ---No valid license
19 ---Invalid license
20 ---Illegal license
21 ---Invalid operation
22 ---SSL connection required