I am designing a Fixed type HEx i.e Fixed tubesheet,tubesheet type-b.(ASME UHX)
In calculation, the value of "Diameter of Channel Gasket Load Reaction" 'ac' is shown as zero.what may be the reason behind it?The extract is shown below:

...Compute the Ratio [Rhoc]:
= ac / ao = 0.0000 / 195.7000 = 0.000000

Please suggest if i should provide more details regarding above problem.
The extract is reproduced below:
The problem is on the last line:
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Results for ASME Fixed Tubesheet Calculations for Configuration b,
Results for Tubesheet Calculations Original Thickness :
UHX-13.5.1 Step 1:
Compute the Tube Expansion Depth Ratio [rho]:
= ltx / h ( modified for corrosion if present )
= 35.0000 / 52.0000 = 0.6731 ( must be 0 <= rho <= 1 )
Compute the Effective Tube Hole Diameter [d*]:
= Max( dt - 2tt*( Et/E )( St/S )( rho ), dt - 2tt)
= Max( 25.4000 -2*2.1080 *(1968885 /1968885 )*
( 1202 /1406 )*(0.673 ), 25.4000 -2*2.1080 )
= 22.9738 mm
Compute the Equivalent Outer Tube Limit Circle Diameter [Do]:
= 2 * ro + dt = 2 * 183.000 + 25.400 = 391.400 mm
Determine the Basic Ligament Efficiency for Shear [mu]:
= (p - dt)/p = (31.7500 - 25.4000 )/31.7500 = 0.2000
Compute the Equivalent Outer Tube Limit Radius [ao]:
= Do / 2 = 391.4000 / 2 = 195.7000 mm
Compute the Effective Tube Pitch [p*]:
= p / sqrt( 1 - 4 * min( AL * CNV_factor, 4*Do*p)/(Pi * Do²) )
= 31.7500 / sqrt( 1 - 4 * min( 0.00 *100.000 , 4*391.400 *31.750 )
/ ( 3.141 * 391.400²) )
= 31.7500 mm
Compute the Effective Ligament Efficiency for Bending [mu*]:
= (p* - d*) / p* = (31.7500 - 22.9738 ) / 31.7500 = 0.2764
Compute the Ratio [Rhos]:
= as / ao = 220.0000 / 195.7000 = 1.124170
Compute the Ratio [Rhoc]:
= ac / ao = 0.0000 / 195.7000 = 0.000000
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There was a bug in my software. The matter has been resolved.
Thank you all.