I have a strategy developed with SharpDevelop that produces 720 lines of PrintDebug output including lines that specify the exact buy and sell calls to WealthLab. One computer works as expected and lists trades but the other computer produces the same debug output but with the exception of the following error at the top and doesn't list trades:

Error processing symbol IWZ Object reference not set to an instance of an object

IWZ is the last symbol in the dataset. The output also includes a PrintDebug statement at the end of the Execute() method that shows up in the debug output on both computers. So, as far as I can tell both systems execute my strategy code completely and in the same way.

The strategy works fine on both computers if ran on a daily dataset. But if it is run on an intraday data set it will by design also utilize daily data from a different dataset that matches the symbols in the current data set as follows (some code excluded).

CODE:
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Maybe you could try reloading IWZ data?

I removed the whole Application Data\Fidelity Investments\WealthLabPro\1.0.0.0\Data\FidelityStaticProvider directory. The updated all the data. Didn't help.

It now works OK on 2 of 3 computers.

For next time: to refresh data for a single symbol/scale, right click its chart and select "Reload Chart History". The entire history will be refreshed no matter the selection in the Data Loading control.

Interesting problem though, so it would be good to isolate it. Since you've got more than 1 computer, did you know that you could relocate your Fidelity Price and Fundamental data to a shared directory? Then you'd only have to update the data only once, and, we could immediately reject the idea that data were the problem.

See User Guide: Data > Data Manager > Symbol Management > Relocate Data