Error 550: Access is denied.
Error 550: Requested action not taken: file unavailable.
Error 550: The system cannot find the path specified.
If so, you may want to check your FTP Publishing setting. The FTP Path setting points to the location of your blog, relative to the root folder in the FTP server.
If the value for your FTP Path is "/", you should change it to ".", or possibly vice versa. Some servers require a setting of "/", which points to the absolute path of the root folder on the server; others require relative paths, such as ".", which points to the FTP root. This issue is discussed in Blogger Help Group: Publishing Trouble Bizarre Blogger Publishing Problem, help!!, and in my article Path Variances When Publishing By FTP.
We've noted in some discussions that, after you change the path to ".", for instance, the Blogger script may change the setting to "./", or even "/". But your initially changing it to "." appears to be a key step, nonetheless. Save the setting, Republish, and test.
Besides the Publishing FTP Path, which indicates where the main blog is stored, there are additional settings, of equal importance. Blogger Help: What is the FTP path? discusses this, and more, in greater detail.
You may also find Microsoft Error message in IIS: "530 User