Make sure you are not using an old shortcut to get to your email. Try this one
Hi - Iwent via the BT Home page / Email, composed the new email but couldn't attach a file.
Tried again using Chrome - no problem. Retried in IE11 - still not working. ????????????
There seems to be some problems with IE11 and BT pages. Try using IE11 in compatability mode. If you look at the address box you will see what looks like a torn page, click on that then try.