That's a hang, and to be useful we need the entire hang report. They are very difficult to interpret, though, at least for me, so it helps to also force a crash. See John's instructions at Adobe Forums: InDesign CS5.5 Not Responding
It might help if you do a Save As in Word after accepting all changes to get as clean a file as possible to start, and trying RTF or the other flavor of Word file (.doc/.docx) can sometimes help, too.
I think I figured out the cause of this (occurs on two different machines, one Mac one Windows 7, so I'm sure it's something about Indesign's handling of the file).
I think it was related to a section where a thin text frame, an image in the master page set to 'text wrap' and a section of text with two beefy footnotes very close together caused Indesign's paragraph placement algorithim to get stuck in some kind of loop, trying to move the breaks to solve one problem, getting in another, trying to solve that, and so on.
I'll try to get some proper error reports rather than hang reports when I'm not chasing a tight deadline (these things always happen at the worst times...), would be nice to confirm that's the cause. In the short term, I've moved the frames in what I think is the problem area and it seems (touch wood) to be okay now.
Just today I saw the same "hang" on a large InDesign file with hundred of footnotes and about 200 pages once imported from a word file.
I cannot tell about the real cause. Just want to report an observation:
The hang occured after I tried to redirect the main text thread through a new text frame in the middle of the thread by clicking inside a new single, not threaded text frame with the loaded text curser. The curser was loaded from clicking the out-port of one of the text frames of the main thread.
Originally that happened with an InDesign CS5 (7.0.4) file. Save As after the hang (forced crash) did not help. Exporting to IDML, reopening in InDesign CS5 or even InDesign CS6 (8.0.1) did not help.
Finally I decided to move two text frames (initially I needed two new text frames in the middle of my main thread) from one spread over to the page I wanted the new text frames added, deleted the now empty spread and just worked on…
However, I'm sure that every time I want to add a new text frame in the middle of the large text thread, InDesign will hang again…
There were no issues adding text frames at the end of the main thread…