Confused about why Function won't compile in ST

Hello.  I am using Scout 5.4 and have the following functions.  I cannot understand why Function FillCDATA won't compile with the following error.

Error 12:45:43 Comms(61) : 6034 :Variable "ReceiveBuffer" cannot be written; transfer to function (block) reference parameter not permitted

ReceiveBuffer is only VAR_INPUT so why does it need to be written?

Any clues or suggestions are much appreciated.  I realise that perhaps I could convert straight to LREAL from the byte array but there are some legacy issues which might prevent me from doing that.  And this is now a matter of principle!

Rich

This is only my guess. For definitive answer you probably should contact the Support.

There must be an error in the compiler. ARRAY[..]OF seems to be passed as a reference. The compiler treats a reference as VAR_IN_OUT and requires its actual parameter to be writable. But the ReceiveBuffer is an INPUT which is not writable and the compiler misses the fact that it is also a reference.

Declaring the ReceiveBuffer as a VAR_IN_OUT makes the code compilable.