I've had this for several days.
My button for weapon swap has been reset to the default bind. If you have changed your keybind for weaponswap, i'd suggest looking if the binding is still correct.
I get this a lot lately. A LOT! I get the message at the top of my screen "You cannot swap weapons now" and I just stand there unable to cast or anything. Eventually it 'catches up' and I can swap or cast. VERY bad.
It happen often when you are using 2 weapons and 1 two-hand weapon. I had it with restorations staff and 1h/shield.
Unslot all weapons AND skills.
Switch weapon set 1 with weapon set2 (so in my case, rest staff where shield/sword and those two to replace staff)
No matter how idiotic it sound, it helped me and few people i know. Only problem is that on character selection screen my templar, no matter what, is always wielding restoration staff...Even if i take it off before relog/log off...But thats not really big issue.
Since iv done that, never had bug with weapon switch again, but if i only try to return to original setting(shield/sword as set1), bug is back...