Cant "Save Project as"? Help please

Hi, only been using audacity for a while, and i have saved about 3 files with it, but when i went to save the fourth i got an error message.

The error message gave the file destination and save audacity could not save “project name” and continues by saying “it is not writeable or the disk is full”

My disk has loads of free space so it isn’t that.

Is this a new problem or is there a solution, would appreciate your feedback guys, Thanks.

You may be using an invalid name. Watch out for “special” characters. a-z, A-Z, 0-9, - _ and are safe. Other characters such as .,!"£$%^&*()_?/… can cause problems.
Also watch out for weird characters in the metadata (if in doubt, open “File > Metadata Editor” and clear the metadata.)