Sporadic error in raster display mode

[vijayiyer05]

Rarely during raster display mode operation, an error occurs:

Subscript indices must either be real positive integers or logicals.

Error in spoke.SpikeGrid/zprvRefreshRasterGrid (line 2183)
                [uniqueStimNums,~,orderedStims] = unique(obj.spikeData{c}.stimNums(plotSpikeIdxs),'sorted'); %orderedStims has same length as plotSpikeIdxs

Error in spoke.SpikeGrid/zcbkTimerFcn (line 1512)
                    obj.zprvRefreshRasterGrid(chanNewSpikes);

Error in spoke.SpikeGrid>@(varargin)obj.zcbkTimerFcn(varargin{:}) (line 258)
            obj.hTimer = timer('Name','Spoke Waveform Grid Timer','ExecutionMode','fixedRate','TimerFcn',@obj.zcbkTimerFcn,'BusyMode','queue','StartDelay',0.1);

Error in timer/timercb (line 30)
    		feval(val{1}, obj, eventStruct, val{2:end});

Error in timercb (line 13)
timercb(t, varargin{2:end});