When trying to Get or Checkout files from the Vault this error can occur...
There may be multiple causes to this issue, but the underlying issue is that something has blocked acces to certain vault client system files. This can be security software and a few reports have come in to Autodesk Support and the Vault Forum.
One of our partners realised that the issue was caused by an update to the free Anti Virus Software, AVG. They found that uninistalling AVG solved the issue, but this was not really acceptable to the customer and they then found out that they just needed to disable the LinkScanner feature within AVG.
Thanks again for the tip Rob from M&M UK!