evaluation – Running .m file from Mathematica notebook

I have use the following command to save a table called “matrix_name” as a .m file named “matrix.m”:

Save["matrix.m", matrix_name]

After this file is created, I try to run it from another mathematica notebook using the following command:

<< matrix.m;

but I get the message

Get: Cannot open matrix.m

Why is this happening?