ASPX Webform write to text file

I'm trying to write to a text file when user clicks on a button on an ASPX page but it does not write to file also, does not return any errors. I'm using following code:

but if i try to read the file using the following code it works:

I have checked security permissions of the folder everyone has access to reading and writing. Anyone know what might have cause this issue or a better way to approach this?

Thanks