Issue:
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iProcess Objects Server returns SAL System Error whenever a queue is accessed and the swentobjsv01.log shows the following type of error:

04908|00298|11/08/2018 16:21:31.290|00010000|ERROR|error in salq_list_open (-2)
04908|00298|11/08/2018 16:21:31.290|00010000|ERROR|get_wqs_session() returned an error, qlistsh = 0, err=-2
04908|00298|11/08/2018 16:21:31.290|00010000|ERROR|qquery_win_setup() returned an error, queuename = MYQUEUE@MYNODE, rc = -2
04908|00298|11/08/2018 16:21:31.306|00010000|ERROR|process_transaction() failed, rc=-2, Message Code(QQW)

Environment:
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TIBCO iProcess Objects Server Version: i11.6(0.0) 
TIBCO iProcess Engine Version: i11.6-o(0.2)
OS: Windows or UNIX

Cause:
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Reviewing the DEBUG from the WIS (with swadm set_attribute 0 WIS 0 DEBUG ALL=255,MAXSIZE=50000000,ONFULL=SAVE enabled) may show that case fields are being included in the filter string used when the work queue is requested by the client application:

[T=01398]181114155140.095999:T064: wis_filter_init(): parsing 'SEGMENT="THISVALUE" AND DATE_IN=!01/08/2016! AND DATE_OT=!01/08/2017!'
[T=01398]181114155140.096205:E004: ==>sal_expression_parse()
[T=01398]181114155140.096501:E004: sal_expression_parse(): parsing 'SEGMENT="THISVALUE" AND DATE_IN=!01/08/2016! AND DATE_OT=!01/08/2017!'
[T=01398]181114155140.096818:E004: => lsal_exp_schk(SEGMENT="THISVALUE" AND DATE_IN=!01/08/2016! AND DATE_OT=!01/08/2017!)
[T=01398]181114155140.097096:E004: <= lsal_exp_schk() - ret = -1
[T=01398]181114155140.097310:E001: sal_expression_parse(): lsal_exp_schk() failed for 'SEGMENT="THISVALUE" AND DATE_IN=!01/08/2016! AND DATE_OT=!01/08/2017!'
[T=01398]181114155140.097517:E004: <==sal_expression_parse()
[T=01398]181114155140.097726:T001: wis_filter_init(): sal_expression_parse() failed: -2

The fields shown above in the filter string (taken from the wis01.log file) show that SEGMENT, DATE_IN and DATE_OT are expected to be found in the list of Case Data Queue Parameters (CDQP) for the work queue.  The WIS cannot parse the expression as the case fields used are not defined as CDQPs and therefore the error -2 is returned.