These are tough problems to troubleshoot. For me, they've always been some small part of a variable or an expression. You've probably looked at the following but just in case... 🙂
I tried to change this to
"\\D-fs11\\spar-it\PROJECTS\\1 Active Projects\\DATA WAREHOUSING PROJECT\\Development\Extract_To_CSV\\"+@[User::DFES_NAME_DATE_File_Name]+".csv"
Notice the single backslash. That would probably lead to the token not recognized message. [Edit note:] My attempts to highlight the backslash aren't working very well. It's between 'Development' and 'Extract_To_CSV'.
I then tried using another variable as the folder name so used the variable @Folder_Name which was already set with the actual folder name. This seemed to be good but when I ran it, the file names were created with [User::DFES_NAME_DATE_File_Name] twice but the first one was the same one every time and the second one was looped so this completely lost me.
I fought through a loop naming problem like this just recently. It turned out that I had added part of the expression for the name in two separate places, once in the variable expression for the file name and once in the actual final file name (including folder path) . So at each loop, each place was adding to the final name. Don't know if that's what happened here but it sounds similar.