Every now and again I get infuriated by our Microsoft Office SharePoint Server (2007) platform as it prompts for credentials (before failing to authenticate and repeating the process) when I go to open a document library in Windows Explorer mode.  Today I found the cause of that issue.

I’d been working at Microsoft’s offices yesterday and had disabled the proxy server settings in my browser.  After returning home and VPNing to our network, I was able to access both Internet and intranet resources as normal and I forgot about the proxy server change. Only when trying to work out why I was being asked for authentication as I tried to use SharePoint in Windows Explorer mode did I remember to turn it back on again – after which everything worked as it should.

It may be peculiar to our infrastructure, or it may be a wider issue that’s worth mentioning so, if you experience authentication issues when trying to open a SharePoint library in Windows Explorer mode, double-check your browser’s proxy server settings!