When using Hotmail on my Macbook Pro, I can't attach files of any type.

When writing a Hotmail email, I can't attach files of any type. This happens only on my Macbook Pro, not my iMac. the last time I was successfully able to attach files to a Hotmail email on my Macbook Pro was on the 1 December 2011. Since then, when I click on Attachment, a go to the folder where the document is, click on it and then only get the option to OPEN, rather than CHOOSE. When I click on OPEN, after a while I get an error message "Attachment Id has bad file format".