Yes, it is a problem with IE.
The same thing happened to my VA as well.
Whenever he wanted to post something on my fanpage, it didn't allow him.
On the other hand, I didn't had any issues while doing the same from my end.
So I asked him to clear cache, change the browser and it worked.
On the other hand, you both can use Hootsuite to schedule updates to your fanpage.
It is a great tool to automate some of the tasks.