Here's a very real possibility for your hanging cfdocument: are you running the ColdFusion Standard edition license?

If so, you probably had another request running that was ALSO doing either a cfdocument or any of several other CFML tags which are single-threaded (with each other) in that edition. If such another request was running long--taking a long time to do a cfdocument itself, for instance--then that will have held up even this simplest cfdocument test you had. And tour restart of CF killed that other long-running request, thus allowing yours to run as expected.

(I realize this question is several years old, and the asker may have moved on long ago. I am offering this now as much for others who may find/have the same question.)

To clarify, starting with CF8, Adobe implemented something called the Enterprise Feature Router--in the ColdFusion Standard edition license. It does NOT apply to the ColdFusion Enterprise or free Developer or Trial editions. With the EFR, all requests that use any of several documented features are single-threaded: only one request at a time can run ANY of those features.

Adobe never documented the tags, but they list several "features" which show being "restricted" in a column of the CF Buying Guide document. See the paragraph below the table of features, which says:

Restricted features in ColdFusion Standard Edition: Enterprise features run through the Enterprise Feature Router (EFR). These features run in the Standard edition. However, all features running through the EFR are limited to one shared simultaneous request.

Among the most common tags (or their script equivalents) where people hit this issue are indeed CFDOCUMENT, and another is the related CFHTMLTOPDF. Still others are less-used: including CFPRINT and CFPRESENTATION. And while the buying guide refers to "pdf manipulation" as one of the "restricted" feature, in have not found any of the many CFPDF tag's actions to be EFR-limited.

Bottom line: if any one request takes a very long time to run--while running ANY such a "restricted" tag--then that request will hold up ANY OTHER requests trying to run at the same time, if those requests also try to run ANY of these "restricted" tags.