Root Restoring Bloatware ; Fail?

[Tumeg]

I am trying to restore the Blockbuster app (the only bloatware I "removed", and need it back so I can attempt to update my phone again).
I am using these steps; [How-To] Reinstall Bloatware with 'System Application' Properties - Android Forums

Trying to "paste" the Blockbuster.apk into "system/app" using Root Explorer, and I get a warning saying "You cannot paste here because the file system is read-only."

Any advice? Am I doing something wrong?

EDIT: I figured it out. I needed to tap "Mount R/W" on the top of Root Explorer.