Possible cause for years old .NET DLL which uses imports from mclmcrrt711.dll and a second Matlab Compiler produced dll to suddenly start producing bad string data?

The subject C# DLL has not been touched in several years. Its functional purpose is simply to write a .mat file of data (nested cell structure) and also to load the .mat file to produce a Matlab figure and save it to a .png file.

The subject DLL imports from two dlls (which also have not been touched for several years) * mclmcrrt711.dll (imports below)

       #region Matlab MCR Imports

        #region Data Functions

        [DllImport("mclmcrrt711.dll")]
        internal static extern IntPtr mxCreateCellMatrix_730_proxy([In] Int32 mxRows, [In]Int32 mxCols);

        [DllImport("mclmcrrt711.dll", CharSet = CharSet.Ansi)]
        internal static extern IntPtr mxCreateString_proxy([In]Char[] CharStr);

        [DllImport("mclmcrrt711.dll")]
        internal static extern IntPtr mxCreateDoubleScalar_proxy([In]Double value);

        [DllImport("mclmcrrt711.dll")]
        internal static extern IntPtr mxGetCell_730_proxy([In]IntPtr mxArray, [In]Int32 mwIndex);

        [DllImport("mclmcrrt711.dll")]
        internal static extern void mxSetCell_730_proxy([In]IntPtr mxArray_Target, [In]Int32 mwIndex, [In]IntPtr mxArray_Value);

        [DllImport("mclmcrrt711.dll")]
        internal static extern Int32 mxGetN_proxy([In]IntPtr mxArray);

        [DllImport("mclmcrrt711.dll")]
        internal static extern Int32 mxGetDimensions_730_proxy([In]IntPtr mxArray);

        [DllImport("mclmcrrt711.dll")]
        internal static extern Int32 mxGetNumberOfElements_proxy([In]IntPtr mxArray);

        [DllImport("mclmcrrt711.dll", CharSet = CharSet.Ansi)]
        internal static extern Int32 mxGetString_730_proxy([In]IntPtr mxArray, [Out]StringBuilder str, [In]Int32 strlen);

        #endregion //Data Functions

        #region Housekeeping Functions

        [DllImport("mclmcrrt711.dll")]
        internal static extern void mxDestroyArray_proxy([In]IntPtr mxArray);

        [DllImport("mclmcrrt711.dll")]
        internal static extern Boolean mclInitializeApplication_proxy(String options, Int32 count);

        [DllImport("mclmcrrt711.dll")]
        internal static extern void mclTerminateApplication_proxy();

        #endregion //Housekeeping Functions

        #endregion //Matlab MCR Imports

* ThermalModel.dll (a Matlab Compiler produced dll, import below)

       #region Thermal Model Imports

        [DllImport("ThermalModel.dll")]
        private static extern Boolean mlxPlotModel(
            [In]Int32 nArgOut, ref IntPtr plhs, [In]Int32 nArgIn, ref IntPtr prhs);

        [DllImport("ThermalModel.dll")]
        private static extern Boolean mlxSave_input_to_disk(
            [In]Int32 nArgOut, ref IntPtr plhs, [In]Int32 nArgIn, ref IntPtr prhs);

        [DllImport("ThermalModel.dll")]
        private static extern Boolean mlxLoad_saved_input(
            [In]Int32 nArgOut, ref IntPtr plhs, [In]Int32 nArgIn, ref IntPtr prhs);

        [DllImport("ThermalModel.dll")]
        private static extern Boolean ThermalModelInitialize();

        [DllImport("ThermalModel.dll")]
        private static extern void ThermalModelTerminate();

        #endregion //Thermal Model Imports

All of a sudden, all string data contained in the cell structure is corrupted with extraneous characters at the end of the strings.

I am looking for possible causes and if anyone else has run into a similar issue. My suspicion is that something contained in a System Update pushed on network computers from Information Technology is to blame. They typically only push security updates to our computers (I am running the Windows 7 Enterprise OS). This issue has appeared on multiple computers.

Any ideas about a possible cause or how to determine the cause will be much appreciated.

Best regards, Pius