Dear Michael and all others,
I have a similar problem as Swagata, but the link from Michael does not answer this question.
I am working with Matlab R2014b and ADVISOR version 2003-00-r0116 and created a copy of the driving cycle "CYC_HWFET_MTN.m" and "CYC_HWFET.mat". I have only changed the values in CYC_HWFET.mat. Then, I renamed both files to CYC_203_Generic.m and CYC_203_Generic_speed_time.mat and updated the file names in CYC_203_Generic_time.m so that the data from CYC_203_Generic_speed_time.mat can be loaded.
Then, I clicked on "drive cycle" --> "add to list" and chose the new driving cycle to import. But then a similar error as Swagata's error occured:
First a window opened (see attached screenshot please)

and after clicking on "yes", the following lines were shown in Matlab:
[SimSetupFig:cycles_Callback] Error!
Error using evalin
Undefined function or variable 'CYC_203_Generic'.