Unable to copy Campaign Map

[Alfwin]

The Campaign editor fails to save my campaign once I've imported a map, displaying the error: "Unable to copy campaign map from 'C:\users\***\AppData\local\temp\WECampaignMaps00\Hero01a.w3x'". The campaign saves normally if no maps are imported (but that's obviously fairly useless). The campaign is saved to 'C:\users\***\Documents\Warcraft III\Campaigns\HeroAdventure.w3n' and the map I'm importing is saved to 'C:\users\***\Documents\Warcraft III\maps\MyMaps\Campaign\HeroAdventure\Hero01a.w3x'. I don't know if that's in any way important.

I looked around a bit and found only one other report of this error, with no solution on offer. Does anyone know what this is/how to fix it? Thanks!