Error using struct2handle Cannot find an exact (case-sensitive) match

I am runing a gui program developed in an older version of Matlab which was case-insensitive. To run the program, I have changed the upper-case m functions and corresponding fig files into lower cases.

However, there are still such errors as

"Error using struct2handle Cannot find an exact (case-sensitive) match for 'UPPERCASE_GUI'. " 
 
Error using waitfor Cannot find an exact (case-sensitive) match for ...

"The closest match is: lowercase_gui in ..."

It seems the program is still trying to locate the upper case figi file.

How does that happen? Do I need to rebuid the fig files?