2280861 - DB6: CLI0112E Error in assignment with Database error -99999 where accessing SAPTOOLS.DBH_STG_TBSPPRF

In transaction SM21 the following error occurs periodically:

Database error -99999 at FET
> CLI0112E Error in assignment. SQLSTATE=22005 row=1 col=4

In the corresponding dev_wX (Dev. Traces), the error shows up like
--------------------------------------------------------------------------------------------------------------------------------------------------------------
C  *** ERROR in DB6Fetch[/bas/742_REL/src/dbs/db6/dbdb6.c, 4165] CON = 1 (BEGIN)
C  &+     dsql_db6_array_fetch( SQLFetch ): [IBM][CLI Driver] CLI0112E  Error in assignment. SQLSTATE=22005 row=1 col=4
C  &+
C  &+      SELECT DBPARTITIONNUM, MEMBER, SNAPSHOT_TIMESTAMP, BPNAME, sum(POOL_DATA_L_READS), sum(POOL_INDEX_L_READS), sum(P
C  &+     OOL_XDA_L_READS), sum(POOL_TEMP_DATA_L_READS), sum(POOL_TEMP_INDEX_L_READS), sum(POOL_TEMP_XDA_L_READS), sum(POOL_
C  &+     DATA_P_READS), sum(POOL_INDEX_P_READS), sum(POOL_XDA_P_READS), sum(POOL_TEMP_DATA_P_READS), sum(POOL_TEMP_INDEX_P_
C  &+     READS), sum(POOL_TEMP_XDA_P_READS)  FROM SAPTOOLS.DBH_STG_TBSPPRF GROUP BY DBPARTITIONNUM, MEMBER, SNAPSHOT_TIMEST
C  &+     AMP, BPNAME
C  &+       cursor type=NO_HOLD, isolation=UR, cc_release=YES, optlevel=5, degree=1, op_type=18, read_only=0
C  &+
C  &+     Output SQLDA:
C  &+                        1 CT=LONG            T=INTEGER         L=4     P=4     S=0
C  &+                        2 CT=CHAR            T=VARCHAR         L=26    P=26    S=0
C  &+                        3 CT=CHAR            T=VARCHAR         L=128   P=128   S=0
C  &+                        4 CT=DECIMAL         T=DECIMAL         L=12    P=23    S=0
C  &+                        5 CT=DECIMAL         T=DECIMAL         L=12    P=23    S=0
C  &+                        6 CT=DECIMAL         T=DECIMAL         L=12    P=23    S=0
C  &+                        7 CT=DECIMAL         T=DECIMAL         L=12    P=23    S=0
C  &+                        8 CT=DECIMAL         T=DECIMAL         L=12    P=23    S=0
C  &+                        9 CT=DECIMAL         T=DECIMAL         L=12    P=23    S=0
C  &+                       10 CT=DECIMAL         T=DECIMAL         L=12    P=23    S=0
C  &+                       11 CT=DECIMAL         T=DECIMAL         L=12    P=23    S=0
C  &+                       12 CT=DECIMAL         T=DECIMAL         L=12    P=23    S=0
C  &+                       13 CT=DECIMAL         T=DECIMAL         L=12    P=23    S=0
C  &+                       14 CT=DECIMAL         T=DECIMAL         L=12    P=23    S=0
C  &+                       15 CT=DECIMAL         T=DECIMAL         L=12    P=23    S=0
C  &+
C  &+     ABAP location info 'CL_SQL_RESULT_SET=============CP', 323
C  &+
C  *** ERROR in DB6Fetch[/bas/742_REL/src/dbs/db6/dbdb6.c, 4165] (END)
B  ***LOG BY2=> sql error -99999 performing FET [dbds         583]
B  ***LOG BY0=> CLI0112E  Error in assignment. SQLSTATE=22005 row=1 col=4 [dbds         583]
--------------------------------------------------------------------------------------------------------------------------------------------------------------

Systems with the database DB2 for LUW (DB6)

SM21, EWA , KBA , BC-DB-DB6 , DB2 Universal Database for Unix / NT , SV-SMG-SER , SAP Support Services , Problem