On Thu, 24 Jan 2013, Marco Patzer wrote:

> On 2013–01–25 Devendra Ghate wrote:
>
>> Just upgraded context installation( to 2013.01.24 16:47),
>> corrected my MWE and I am still getting exactly the same error.
>
> You're right, it fails here, too. The message got lost in between
> all the tikz log output. On my machine I get:
>
> Package tikz: Error! I did not find the tikz library 'external'. I looked for files named tikzlibraryexternal.code.tex and pgflibraryexternal.code.tex, but neither could be found in the current texmf trees..
>
> And tikz is right with that. There is no such file in the
> distribution. Either the name of this module changed or the file is
> missing in the distribution, I guess.

From the pgf manaul:

32.3 A Word About ConTEXt And Plain TEX

Currently, the basic layer backend \beginpgfgraphicnamed ... 
\endpgfgraphicnamed relies on LATEX only, so externalization is only 
supported for LATEX yet.

Perhaps you can use the filter module for externalizing tikz figures.

Aditya