Thank you very much - I am currently follow your step-by-step guide. Much appreciated.
About the error. I actually fixed the error a while ago - I was kept busy with the VS2019 story. The error is not method, class, extension class, project, solution, model, package, VS usage data or VM specific (I tried editing without an open solution as well as a new class in a different model, cleared usage data and also tried on another VM). It is flat out caused by code/text arrangement (the only thing I did not check is the element's model's package references). But then I am assured by my hypothesis by the comments in the link I supplied in the OP. So the solution was to re-arrange the code.
I think I can actually guarantee that it will happen on any VM (in VS2015 of course). Create a class. The name does not matter - for the example I created XYZClass. Then paste this code:
class XYZClass
{
void updateSum(TransDate _transDate, LedgerPostingType _postingType, RefRecId _mainAccount, DimensionDefault _dimensionDefault, CurrencyCode _currencyCode, AmountCur _amountCur, NoYes _isFactorOk, RefRecId _clearingAccount, PaymTermId _paymentTermId, PaymTermId _clearingPeriod, PaymDayId _paymentDay, TransDate _fixedDueDate, ExchangeRateTypeRecId _exchangeRateTypeRecId)
{
}
}
The code arrangement is not BP - leave it like that. Save the file, close it, re-open it and then start typing in the method. VS2015 will crash:
It can be fixed by splitting the parameters in the method header (as prescribed by BP).
