When pump flow was changed,unsteady flow analysis meets trouble

[Jack smith ASA]

When pump flow was 2.5 cms,it run well.But when I changed it to 1.5 cms,problem encountered.
Any help would be greatly appreciated.

Geometric Preprocessor Version 4.1.0 Jan 2010
Finished Processing Geometry
Performing Unsteady Flow Simulation Version 4.1.0 Jan 2010
**** Solution Solver Failed ****
Minimum error exceeds allowable tolerance at 13NOV2011 0926
i 1 10.4*
WARNING!
***** Extrapolated above Cross Section Table at: *****
1 1-5 from R.S. 41.8* to 41.6*
1 1-5 R.S. 39.62
1 1-4 R.S. 39.6*
1 1-4 from R.S. 38.6666* to 38.3333*
d 1 from R.S. 4.6* to 4.4*
d 1 from R.S. 3 to 2.5*
2 1-3 R.S. 23.8*
2 1-3 from R.S. 22.8* to 21.8*
e 1 R.S. 4.8*
i 1 from R.S. 15 to 12.2*
i 1 from R.S. 11.6* to 10.2*
i 1 from R.S. 9.2* to 8.4*
i 1 from R.S. 7.8* to 7.2*
1 1-8 R.S. 36.4*
1 1-8 R.S. 35.8*
1 1-8 R.S. 35.4*
1 1-8 R.S. 35
2 1-5 R.S. 21.2*
2 1-5 R.S. 20.8*
2 1-5 R.S. 19.4*
2 1-5 R.S. 19
2 1-5 from R.S. 18.6* to 18.4*
j 1 from R.S. 1.125 to 1
The maximum water surface error was 2580.164
and occurred at 13NOV2011 09:27:15
Finished Unsteady Flow Simulation
Writing Results to DSS
Finished Writing Results to DSS
Reading Data for Post Process
Simulation went unstable at: 13Nov2011 09:27:15
Resetting post process profiles to end at: 13NOV2011 0927
Running Post Processor Version 4.1.0 Jan 2010

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