You had probably shadowed the function class() with some variable by the same name -- which is something you should avoid.
which class -all
built-in (/MATLAB/toolbox/matlab/datatypes/class)
/MATLAB/toolbox/matlab/graph2d/@scribehandle/class.m % Shadowed scribehandle method
/MATLAB/toolbox/instrument/instrument/@udp/class.m % Shadowed udp method
/MATLAB/toolbox/instrument/instrument/@i2c/class.m % Shadowed i2c method
/MATLAB/toolbox/instrument/instrument/@gpib/class.m % Shadowed gpib method
/MATLAB/toolbox/instrument/instrument/@icdevice/class.m % Shadowed icdevice method
/MATLAB/toolbox/instrument/instrument/@visa/class.m % Shadowed visa method
/MATLAB/toolbox/instrument/instrument/@tcpip/class.m % Shadowed tcpip method
/MATLAB/toolbox/instrument/instrument/@Bluetooth/class.m % Shadowed Bluetooth method
/MATLAB/toolbox/instrument/instrument/@icgroup/class.m % Shadowed icgroup method
/MATLAB/toolbox/matlab/serial/@serial/class.m % Shadowed serial method
help class
CLASS Return class name of object.
S = CLASS(OBJ) returns the name of the class of object OBJ.
Possibilities are:
double -- Double precision floating point number array
(this is the traditional MATLAB matrix or array)
single -- Single precision floating point number array
logical -- Logical array
char -- Character array
cell -- Cell array
struct -- Structure array
function_handle -- Function Handle
int8 -- 8-bit signed integer array
uint8 -- 8-bit unsigned integer array
int16 -- 16-bit signed integer array
uint16 -- 16-bit unsigned integer array
int32 -- 32-bit signed integer array
uint32 -- 32-bit unsigned integer array
int64 -- 64-bit signed integer array
uint64 -- 64-bit unsigned integer array
<class_name> -- MATLAB class name for MATLAB objects
<java_class> -- Java class name for java objects
%Example 1: Obtain the name of the class of value pi
name = class(pi);
%Example 2: Obtain the full name of a package-based java class
obj = java.lang.String('mystring');
class(obj)
For classes created without a classdef statement (pre-MATLAB version
7.6 syntax), CLASS invoked within a constructor method creates an
object of type 'class_name'. Constructor methods are functions saved
in a file named <class_name>.m and placed in a directory named
@<class_name>. Note that 'class_name' must be the second argument to
CLASS. Uses of CLASS for this purpose are shown below.
O = CLASS(S,'class_name') creates an object of class 'class_name'
from the structure S.
O = CLASS(S,'class_name',PARENT1,PARENT2,...) also inherits the
methods and fields of the parent objects PARENT1, PARENT2, ...
O = CLASS(struct([]),'class_name',PARENT1,PARENT2,...), specifying
an empty structure S, creates an object that inherits the methods and
fields from one or more parent classes, but does not have any
additional fields beyond those inherited from the parents.
See also ISA, CLASSDEF, STRUCT, SUPERIORTO, INFERIORTO.
Documentation for class
doc class
Other functions named class
Bluetooth/class icdevice/class serial/class udp/class
gpib/class icgroup/class tcpip/class visa/class
i2c/class scribehandle/class
Since said variable is now missing and not shown in the provided code excerpt, you'll have to figure out where it went.