Can someone please explain to me the meaning of the following exception. When i see this exception in hansa.log, the system hangs and I have to restart it.

2018-11-30 10:03:59 (-1) /THREAD(2) SOCKET [60] os fd 890 got exception, removed listener
2018-11-30 10:04:01 (-1) /THREAD(2) SOCKET [143] os fd 4344 got exception, removed listener
2018-11-30 10:04:02 (-1) /THREAD(2) SOCKET [137] os fd 4337 got exception, removed listener
2018-11-30 10:04:04 (-1) /THREAD(2) SOCKET [189] os fd 4395 got exception, removed listener
2018-11-30 10:04:06 (-1) /THREAD(2) SOCKET [136] os fd 4336 got exception, removed listener
2018-11-30 10:04:09 (-1) /THREAD(2) SOCKET [150] os fd 4353 got exception, removed listener
2018-11-30 10:04:11 (-1) /THREAD(2) SOCKET [152] os fd 4355 got exception, removed listener
2018-11-30 10:04:13 (-1) /THREAD(2) SOCKET [177] os fd 4381 got exception, removed listener
2018-11-30 10:04:18 (-1) /THREAD(2) SOCKET [156] os fd 4359 got exception, removed listener
2018-11-30 10:04:24 (-1) /THREAD(2) SOCKET [196] os fd 4402 got exception, removed listener
2018-11-30 10:04:24 (-1) /THREAD(2) SOCKET [195] os fd 4401 got exception, removed listener
2018-11-30 10:04:26 (1) KS Level 1 processed -61.63 percent, found 394 376 records
2018-11-30 10:04:30 (-1) /THREAD(2) SOCKET [159] os fd 4362 got exception, removed listener