I know that this is a bit of an old thread, but this is what we uncovered that corrected this issue on a permanent basis on several of our servers...

First off, this is not actually a SQL Server issue, but one for the OS. Install the ODBC fix from KB940046 (http://support.microsoft.com/kb/940046). There is a known issue with ODBC that affects 3 of the extended stored procedures in SQL Server 2005 (xp_delete_file, xp_enumerrorlogs, and xp_readerrorlog). If you apply the fix from this KB on your server(s), the error will no longer present itself.

Note: your ODBC drivers may currently have a higher build number than the fix has, apply it anyway, it is a QFE build and has not been (and will likely never be) folded into a GDR build.