Why am I unable to start FDATool in the Signal Processing Toolbox 6.1 (R13+)

Why am I unable to start FDATool in the Signal Processing Toolbox 6.1 (R13+) when the DSP Blockset and/or Filter Design Toolbox license has expired? I receive the following errors when I try to start FDATOOL after the DSP Blockset license has expired. However, the FDATOOL is part of the Signal Processing Toolbox and should be independent of the DSP Blockset license.   ??? Error using ==> feval Undefined function 'fdplugin'. Error in ==> C:\Matlab6p5\toolbox\signal\sigtools\addplugins.m On line 44 ==> fcnStruct = feval(pluginStruct.plugin{j}); Error in ==> C:\Matlab6p5\toolbox\signal\sigtools\private\fdatool_sidebar.m On line 27 ==> addplugins(hSB); Error in ==> C:\Matlab6p5\toolbox\signal\sigtools\private\addcomponents.m On line 9 ==> fdatool_sidebar(hFDA); Error in ==> C:\Matlab6p5\toolbox\signal\sigtools\fdatool.m On line 32 ==> addcomponents(hFDA);