Thanks for your replies.
@ Peter Spier
All of my frames have 2 columns, and the error only occurs when switching from span, to single. This is the log from the Event Viewer, although it doesn't provide much to work with:
Faulting application name: InDesign.exe, version: 8.0.1.406, time stamp: 0x50335e39
Faulting module name: TEXT.RPLN, version: 8.0.1.406, time stamp: 0x50336251
Exception code: 0xc0000005
Fault offset: 0x000520a7
Faulting process id: 0x508
Faulting application start time: 0x01ce3d1c8246b019
Faulting application path: C:\Program Files (x86)\Adobe\Adobe InDesign CS6\InDesign.exe
Faulting module path: C:\Program Files (x86)\Adobe\Adobe InDesign CS6\Required\TEXT.RPLN
Report Id: d5aab10a-a90f-11e2-93b3-50e5494282ba
@ Joel Cherney
Unfortunately the import style trick didn't work, but it was a good idea. Like you suggested, I will be staying away from the span options from now on.
I ended up deleting all of the paragraph styles to get things moving again.
Thanks again,
Ben