Looks like this is what triggers an error in my document too. [Ref. 
"Broken Nightly 2012.07.08 20:02 - unpredictable errors on blank lines"]

Commenting out all floats got rid of the error.

On 09/07/12 09:50, Meer, H. van der wrote:
> Is the following a known issue with this beta? When a float block moves the error appears:
> ConTeXt  ver: 2012.07.04 23:48 MKIV  fmt: 2012.7.6  int: english/english
>
> floatblocks     > 1 placed
> floatblocks     > 1 saved
> pages           > flushing realpage 5, userpage 1
> floatblocks     > 1 moved
> floatblocks     > 2 moved
> ! Extra \fi.
>
> A short example is difficult to procure, but adding one line of text, inducing the float to move, triggers the error.
>
> Hans van der Meer
>
>
>
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