Reports can fail to produce output files when the file name and path is greater than 260 characters.
Dependent on where you run them you may or may not get an error message.
Running the report within a report runner preview control gives a message that the output report file could not be accessed.
To check how long your report is make a note of the length of the full file path to "Report Files" and a date folder within:
FullPath = "C:\CallScripter\CallScripter Live\CallScripter Data\Reports\Report Files\2015-05-25"
For the file name use the script name, a seperator of " - ", the report name, up to 7 characters for the Report ID (up to 9999) and surrounding brackets " (52)", a seperator of " - ", a 40 character guid (40 random characters) and the file extension. to give:
FileName = "Script Name HERE - Report Name HERE (52) - 40 CHARACTER GUID IN HERE.csv"
When you add the FullPath and FileName together in to a vlid path you get the complete file name and path. this must be below 260 characters.
ie: C:\CallScripter\CallScripter Live\CallScripter Data\Reports\Report Files\2015-05-25\Script Name HERE - Report Name HERE (52) - 40 CHARACTER GUID IN HERE.csv