Slightly odd behaviour with matlab - Any chance on someone checking the code?

I've written the following class in matlab as a wrapper for interacting with a U3. It works 99% of the time, but occasionally it the U3 does not respond by outputing the appropriate analog or digital steps. I can't see what the problem is. I was hoping there was a chance someone could look over it.

The class is below... the code snippet that operates it is:

        lj = MyLJ([4], [6, 7], [], [0]);

        lj.write_analog(5*randn(1,1));

        lj.write_digital( logical(1) );

        %some function that takes 3 seconds to operate

        lj.write_digital(logical([0, 0]));

        lj.write_analog(0);

classdef MyLJ

    properties

        ljasm

        ljudObj

        ljhandle

        

        num_input_chans

        

        

        dig_in_chans

        analog_in_chans

        

        dig_out_chans

        analog_out_chans

    end

    

    methods

        function obj = MyLJ(dig_in_chans, dig_out_chans, analog_in_chans, analog_out_chans)

            if intersect(dig_in_chans, dig_out_chans)

                error('Overlap between digital in and out pins. Pin cannot be both input and output')

            end

            

            %Make the UD .NET assembly visible in MATLAB

            obj.ljasm = NET.addAssembly('LJUDDotNet'); 

            obj.ljudObj = LabJack.LabJackUD.LJUD;

            

            %Open Labjack

            [ljerror, obj.ljhandle] = obj.ljudObj.OpenLabJack(LabJack.LabJackUD.DEVICE.U3, LabJack.LabJackUD.CONNECTION.USB, '0', true, 0);

            

            %Reset to default

            obj.ljudObj.ePut(obj.ljhandle, LabJack.LabJackUD.IO.PIN_CONFIGURATION_RESET, 0, 0, 0); 

            

            obj.num_input_chans = sum([length(dig_in_chans) length(analog_in_chans)]) ;

            

            %Set up input pins

            obj.dig_in_chans = dig_in_chans;

            obj.config_dig_in(dig_in_chans);

            obj.analog_in_chans = analog_in_chans;

            obj.config_analog_in(analog_in_chans)

            

            %Set up output pins

            obj.dig_out_chans = dig_out_chans;

            obj.analog_out_chans = analog_out_chans;

            

            %Push setup

            %obj.ljudObj.GoOne(obj.ljhandle);

        end

        

        function config_dig_in(obj, dig_in)

           for pin = dig_in

              obj.ljudObj.AddRequest(obj.ljhandle, LabJack.LabJackUD.IO.GET_DIGITAL_BIT, pin, 0, 0, 0); 

           end            

        end

        

        function config_analog_in(obj, analog_in)

            for pin = analog_in

                obj.ljudObj.AddRequest(obj.ljhandle, LabJack.LabJackUD.IO.GET_AIN, pin, 0, 0, 0);

            end

        end

        

        function read = read_all(obj)

            % Read a single value from every analog and digital channel in

            % order, digital channels first, then analog channels.

            

            obj.config_dig_in(obj.dig_in_chans);

            obj.config_analog_in(obj.analog_in_chans);

            obj.ljudObj.GoOne(obj.ljhandle);

            

            read = zeros(1,obj.num_input_chans);

            

            for i = 1:obj.num_input_chans

                if i == 1

                    [ljerror, ioType, channel, dblValue, dummyInt, dummyDbl] = obj.ljudObj.GetFirstResult(obj.ljhandle, 0, 0, 0, 0, 0);

                else

                    [ljerror, ioType, channel, dblValue, dummyInt, dummyDbl] = obj.ljudObj.GetNextResult(obj.ljhandle, 0, 0, 0, 0, 0);

                end

                read(i) = dblValue; 

            end 

        end

        

        function write_analog(obj, analog_vals)

            % Writes to analog channels in order. Can write to just first n

            % channels.

            if length(analog_vals) > length(obj.analog_out_chans)

                error('More values given than analog out channels configured')

            end

            

            for i = 1:length(analog_vals)

                obj.ljudObj.AddRequest(obj.ljhandle, LabJack.LabJackUD.IO.PUT_DAC, obj.analog_out_chans(i), analog_vals(i), 0, 0);

            end

            

            obj.ljudObj.GoOne(obj.ljhandle);

        end

        

        function write_digital(obj, digital_vals)

            % Write digital channels in order. Can write to just first n

            % channels

            if length(digital_vals) > length(obj.dig_out_chans)

                error('More values given than digital out channels configured')

            end

            

            for i = 1:length(digital_vals)

                obj.ljudObj.AddRequest(obj.ljhandle, LabJack.LabJackUD.IO.PUT_DIGITAL_BIT, obj.dig_out_chans(i), digital_vals(i), 0, 0);

            end

            

            obj.ljudObj.GoOne(obj.ljhandle);

        end        

    end

end