HydraCALC is calculating the equivalent lengths wrong 

Revit could not complete the external command... System.NullReferenceException

Revit could not complete the external command... System.ArgumentException

When selecting a vertical pipe/riser nipple hydrapipe, the PROPERTIES window shows "no selection" instead of "hydrapipe"

You may notice that you cannot use the 'change length' command (CL) or cannot rotate riser nipple (RRT)

No error reported for FSC even when maximum length is clearly exceeded

If you view the FSC properties, it's possible the HoseLength and MaxNumberOfBends values are not set.

Welded and Grooved POLs look strange when modeled in Metric units, and their dynamic lengths are reported incorrectly.

Calculation stops at Step 1a.4 - calcing total lengths

There is also Runtime error 5 invalid procedure call or argument 

When raising to 3D, AutoCAD crashes with no error, no warning, it just closes.

You can test this by closing all open drawings then starting a new drawing using the Hydratec template, "Hydracad Imperial Default".

Draw one pipe 10' long (LN command). 

Place a length & 2" diameter on it (SZP command)

Place a 10' AFF elevation mark on it (AFF command)

Start the process of raising to 3D (S3D command).  It will then crash out without warning around step 2 (something about sprinkler heads).

The diameter tag HANDLE is 0000 this number is used to determin if the pipe is sloped - yielding an incorrect pipe length. Move Line / Move Main make the diameter tag HANDLE be 0000

When plotting two viewports, one with center-to-center lengths, and the other with cut lenghts, the riser nipples/vertical pipes will show both, even if your layout tab looks fine.

LAYOUT TAB

PLOT PREVIEW

Hanger length attribute is missing. The hanger inserts only the assembly number even if the HIDE NUMBER box is checked in the Hanger Setup. A V45 hanger block is in the drawing. It has only one attribute value & can display only the number. HydraCAD v50

The last sprinkler head setup as sprigs on sloped pipe will most likely show a cap length shorter than the 'flat' length. For instance, a 3" capped pipe is returning from 3D as 2" rather than a longer length. n/a Plan View n/a

There is a frozen and / or locked HydraCAD layer. or RNs with 0-0 length

Some pipe sizes have the diameter and length attributes switched in their order

Error matching operating head @ (xxxx.xxx, yyyy.yyy) The only option is the OK button. ALSO - The equivalent k-factor for node xxx is not an end point.

When attempting to run AutoLIST, an error message says; Error: Unable to insert cut length dimensions! Unable to insert cut 

You may also see this message;

Re-run Autolist with the drawing starting on the ground, Current run will not include any FSC information in the MISC tab in HydraLIST

Caclulating Total Lengths...

Runtime Error "13"

Type mis-match

Pipe sizes and lengths do not return to drawing. Pipe sizes disaprear

When using Rapid Pipe/Rapid Line/Rapid Main, you do not see the tooltip which indicates your future pipe lengths

When starting AutoCALC, it stops in the v50 Fuel Gauge at step 1a.4 - Calculating Total Lengths. 

Working on the pipe from node xxx to node xxx with a fitting string...

May be followed by a Runtime Error 13 as well