sporadic workplace license error

The system is 800xA 5.1 Rev.D FP4. All is fine but from time to time we get a license error on the last restarted workplace (CLCB01 in this case):

TimeStamp,ErrorCode,LicenseGroup,Feature,Node/Application,MinVersion,MaxVersion
,OptionString,QuantityRequested,QuantityGranted
2016/01/22 23:14:55,0x8004ab81,800XA OPERATIONS,OPERATOR_WPL,CLCB01,5.1,0,,1,0
TimeStamp,ErrorCode,LicenseGroup,Feature,Node/Application,MinVersion,MaxVersion
,OptionString,QuantityRequested,QuantityGranted
2016/01/24 04:15:12,0x8004ab81,800XA OPERATIONS,OPERATOR_WPL,CLCB01,5.1,0,,1,0
2016/01/25 08:10:01,0x8004ab1c,CBA,DUMMYF,PGCB01,6.3,0.0,(null),0,0
TimeStamp,ErrorCode,LicenseGroup,Feature,Node/Application,MinVersion,MaxVersion
,OptionString,QuantityRequested,QuantityGranted
2016/01/25 09:15:03,0x8004ab81,800XA OPERATIONS,OPERATOR_WPL,CLCB01,5.1,0,,1,0
2016/01/25 15:58:49,0x8004ab1c,CBA,DUMMYF,PGCB01,6.3,0.0,(null),0,0
2016/01/26 11:16:58,0x8004ab1c,CBA,DUMMYF,PGCB01,6.3,0.0,(null),0,0
2016/01/26 11:41:03,0x8004ab81,800XA OPERATIONS,OPERATOR_WPL,CLCB03,5.1,0,,1,0
2016/01/26 11:44:44,0x8004ab81,800XA OPERATIONS,OPERATOR_WPL,CLCB02,5.1,0,,1,0
2016/01/26 11:52:31,0x8004ab81,800XA OPERATIONS,OPERATOR_WPL,CLCB04,5.1,0,,1,0
2016/01/26 11:56:45,0x8004ab81,800XA OPERATIONS,OPERATOR_WPL,CLCB05,5.1,0,,1,0
2016/01/26 12:24:01,0x8004ab81,800XA OPERATIONS,OPERATOR_WPL,CLCB06,5.1,0,,1,0
TimeStamp,ErrorCode,LicenseGroup,Feature,Node/Application,MinVersion,MaxVersion
,OptionString,QuantityRequested,QuantityGranted
2016/01/26 14:37:32,0x8004ab81,800XA OPERATIONS,OPERATOR_WPL,CLCB08,5.1,0,,1,0
2016/01/26 15:50:54,0x8004ab81,800XA OPERATIONS,OPERATOR_WPL,CLCB01,5.1,0,,1,0
2016/01/27 13:35:55,0x8004ab1c,CBA,DUMMYF,PGCB01,6.3,0.0,(null),0,0
TimeStamp,ErrorCode,LicenseGroup,Feature,Node/Application,MinVersion,MaxVersion
,OptionString,QuantityRequested,QuantityGranted
2016/01/27 19:15:25,0x8004ab81,800XA OPERATIONS,OPERATOR_WPL,CLCB01,5.1,0,,1,0
2016/01/28 06:37:09,0x8004ab1c,CBA,DUMMYF,PGCB01,6.3,0.0,(null),0,0
2016/01/28 10:21:14,0x8004ab1c,CBA,DUMMYF,PGCB01,6.3,0.0,(null),0,0
TimeStamp,ErrorCode,LicenseGroup,Feature,Node/Application,MinVersion,MaxVersion
,OptionString,QuantityRequested,QuantityGranted
2016/01/29 00:15:24,0x8004ab81,800XA OPERATIONS,OPERATOR_WPL,CLCB01,5.1,0,,1,0

In the license status viewer is nothing to see, in the "running workplaces" all is correct. We have 8 OPERATOR_WPL and 4 REM_OPER_WPL. Client 1..8 running direct, Client 10...13 running remote. Please see details in the attached file.

We have restarted all the clients and we had a look at all the servers if a workplace process may have been in the taskmanager (remaining by error).

Has anyone an idea what could cause this problem?

/Erik