[support] FusionPath problem on update

[Luke]

While updating a D6.20 site via drush, it wants to update fusion:

Fusion                    6.x-1.0         6.x-1.1         Update available

I give it the go-ahead, and receive:

Module fusion path is not available, perhaps the module is enabled 
[error]
but has been deleted from disk.
Cache cleared.
An error occurred at function : drush_core_cache_clear 
[error]
An error occurred at function : drush_pm_updatecode 
[error]
An error occurred at function : drush_pm_update 
[error]

I can't find any references to fusionpath in the fusion release notes, 
source tree, or parts of the handbook which seemed most likely.

Google is turning up zilch.

Thanks for any suggestions!

Luke