This problem affects a multinode environment made of Enteprise Terminal Serever + Enterprise Terminal Server Nodes.

Under some circumstances, it can happen that the session on the node is lost during its creation. Further investigations found that this happen when for some reasons the server daemon on the node suddenly terminates before the new session is stored on disk. The termination of the server daemon is caused by a race condition during the search for the physical display.

When this happens, server logs on the node host reports:
arguments to dbus_message_new_method_call() were incorrect, assertion "_dbus_check_is_valid_path (path)" failed in file ../../dbus/dbus-message.c line 1371.

The process backtrace is:
(gdb) bt
#0  0x00007f8dfe9d7387 in raise () from /lib64/libc.so.6
#1  0x00007f8dfe9d8a78 in abort () from /lib64/libc.so.6
#2  0x00007f8dec0a3655 in _dbus_abort () from /lib64/libdbus-1.so.3
#3  0x00007f8dec09ad0e in _dbus_warn_check_failed () from /lib64/libdbus-1.so.3
#4  0x00007f8dec08aae0 in dbus_message_new_method_call () from /lib64/libdbus-1.so.3
#5  0x00007f8df4f9fb1 in ServerDBusMethod () from /usr/NX/lib/libnxhs.so
#6  0x00007f8df596ec9 in NXDBusSend(char**, char*, char*, char*, char*, char*) () from /usr/NX/lib/libnxhs.so
#7  0x00007f8df59764d in NXExtractDataForSessionByLOG(DbusSession*, char*) () from /usr/NX/lib/libnxhs.so
#8  0x00007f8df597e4a in ServerRetrieveDbusSessionsByLogin1(DbusSession**, int*) () from /usr/NX/lib/libnxhs.so
#9  0x00007f8df59dde9 in ServerGetSessionList(NXSession**, int*) () from /usr/NX/lib/libnxhs.so
#10 0x00007f8df59ef87 in ServerPhysicalSessionMain(int, char**, char**) () from /usr/NX/lib/libnxhs.so
#11 0x00007f8df316d4 in ?? () from /usr/NX/lib/libnxc.so
#12 0x00007f8df20fea5 in start_thread () from /lib64/libpthread.so.0
#13 0x00007f8dfea9f96d in clone () from /lib64/libc.so.6

As a possible workaround, disable the search for physical display by removing the 'physical-desktop' type from the list of values for the AvailableSessionTypes key in server.cfg. Then restart the NoMachine server.