In SharePoint 2007, there are 2 ways to open a folder in Explorer view, in the Actions menu, or through the ‘Explorer view’
However, if you are at a very low level folder and the path of the folder is more than 100 characters, you will get this error message:
I drilled down with the client code and found that it’s because of a Microsoft IE API (httpFolder.navigateFrame) that used by SharePoint (NavigateHttpFolderCore() function in \12\TEMPLATE\LAYOUTS\1033\Core.js) that has the 100 characters limit on the web address (including the starting http://).
The workaround is that users goes to top level folders to open it Explorer view, then navigate to the folder they want to go. When they navigate through the folders within Explorer View, there is no limit on the folder path length.