Please see the link below and the error that this guy got. I am getting the same error when trying to export/import a fairly large string.
Now he found a solution to the problem. I've tried contacting him on getting an answer on how he did this, but was unsuccessful. I was hoping that someone on these forums would be able to help.
(And before anyone mentions it, I do not want to split up my large WeakAura and break it up into smaller strings, personal preference.)