error loading .mat file

Unable to read MAT-file. Not a binary MAT-file. Try load -ASCII to read as text. but on the first iteration it loads this file

[Voss]

Maybe something in your code is overwriting the .mat file (incorrectly) after it is loaded the first time. Can you share the complete code?

[Aditya]

Is it some online file ? What is the size of file ?

[Matt J]

but on the first iteration it loads this file

Why are you loading the same file iteratively? If the contents are changing as a result of the iterations, it is likely that you over-wrote it with a different type of file.