When I run a script I have and do a backtest on all symbols I get the following across about twenty symbols and consistently on the same symbols. However when I run the test individually on each symbol the script runs fine. If I could trap an individual symbol I could debug it, but when it only does it on a general backtest it's hard.

QUOTE:
Error processing symbol ALL Exception from HRESULT: 0x800AC472
Error processing symbol AMC Exception from HRESULT: 0x800AC472

To me HRESULT looks suspiciously like WealthLab itself. Has anyone else seen this kind of error and could point me to the kind of thing to look for in my code?

I've never seen this in Version 5. On the surface, it looks like a COM exception, which probably points to a data adapter or some other component that your code references.

Version 5 it is. I don't reference a COM as such, although I do access Excel via a library in a C# class. And I did wonder about hitting Excel too fast, but then why would either of these raise an exception from HRESULT?

Is there a difference between a backtest on all symbols and running the strategy on a single dataset?

QUOTE:
Version 5 it is. I don't reference a COM as such, although I do access Excel via a library in a C# class

Pardon me, but Excel still lives in the COM land?

Just google for 0x800AC472, and you'll see that "Exception 0x800ac472 when accessing Excel" seems to be pretty common.

Thanks for that. I misunderstood Cone's answer and thanks for the clarity. I'll investigate Excel.