By default, any network drive that times out is “marked as invalid” for 5 minutes (300 seconds), and you’ll see a message like this in the script log:

# INFO : 4000 - Server '\\server' is unreachable. Marked as invalid for the next 300 seconds

The timeout interval is controlled by the environment variable SI_FILEPATH_ACCESSRETRYDELAY.

Setting SI_FILEPATH_ACCESSRETRYDELAY to 0 will force Softimage to always try to access the files on the network drive. That might be useful if your network has extremely poor reliability.

From an XSI mailing list thread about this message, here’s a bit more info about how Softimage resolves paths:

XSI first checks the last path that an image has been found. This
might be offline drive X:. If a drive times out, we don’t try to
check that location for a while because otherwise it’d be really slow.
At this point, XSI resort to searching for the file from the user
path, using its search logic.
So that warning isn’t a problem – unless your “user path” was really
set to X:, in which case, go fix the path in the external file list.
The path where XSI finds the image is called the “resolved path”.

–Luc-Eric