MATLAB Preventing Code Folding

I'm writing a function which is hundreds of lines long and I need it to fold code in order to write it. However, the function suddenly prevented code folding of any kind. All the code folding preferences are set to on and it is the only function which is preventing me from folding code. Does anyone know why this could happen and how to fix it? Thanks.

[Walter Roberson]

That can happen if there is a structure error in your code such as a missing end statement.

[Ephraim Bryski]

Thank you so much! I had two parse errors (an extra end which I added in an attempt to fix the problem and a line which I hadn't finished writing) so it was initially hard to realize what was causing it.