When trying to run the calculation, you get the message, 

"The system flow demand of ### exceeds the maximum rated flow as indicated in the Pump Curve for the pump with the inlet of PI and outlet of PO.  The calculation will not continue"

But your flow is a very large number

When running a Darcy-Weisbach calculation, after changing your k-factor, the program will not ask to Modify K-Factor anymore

The calculation method you have chosen is only a legal calculation method under NFPA 13 rules for anti-freeze systems and requires modified k-factors

Have the k-factors already been modified

When clicking the Calculate button or the OK button from the Pre-Calc Questions window, you get a Runtime-error 5,

Run-time error '5': Invalid procedure call or argument

When editing the cells, you receive the error Run-time error '6', Overflow

When hitting Save, Refresh Drawing or Calculate Results, user gets a Run-time 9 error. AKA Subscript out of Range

When trying to open a calc job using [File|Open], you get a Run-time error '62': Input past end of file

When opening HydraCALC SIZER, you get the error;  Run-time error '53': File not found

Dup Equiv K / Sys Pipe Node

The View button that appears after running a calculation does not do anything

Or you get the error; C:\Windows\system32\Write.exe

'file name asked for does not exist!

No error but the calculation process takes a very long time and is slow.

The process hangs and usually the RAM runs up to 100%.  You'll likely hear the computer's fan rev up.