Assuming these are the instructions you followed from help

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This procedure sets the default folder for opening and saving Microsoft Excel
files.

On the Tools menu, click Options, and then click the General tab.
In the Default file location box, type the path for the folder you want to
display as the default working folder.
For example, type c:\work.

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Has this not been saving since you first installed Excel or is it a recent
development?

What is the current path/folder that will not change?

Are you on a network or standalone system?

This setting is stored in the Registry.

Are you sure your account allows you to save these types of settings.

Gord Dibben  MS Excel MVP