I am running simulations for a slight modification to an existing strategy on 3minute bars and after a few successful iterations I got this message:

"Runtime error: Exception of type 'System. OutofMemoryException' was thrown
at WealthLab.Strategies.MyStrategy.Execute
at WealthLab DataSeries.op Multiply(dataSeies ds1.Double value)
at WealthLab.DataSeries.ctor(dataSeries A 0. StringA 1. Boolean A 2)
at WealthLab DataSeries. b(Int32A0)
at System.Collections.Generic.list 1 set Capacity(int32value)

I can still run other strategy simulations, autotrade is working etc etc

I've tried rebooting

Any idea how I can clear this ?

For the background and possible workarounds, see this section of the Wiki FAQ:
Out of memory problems