Does the filename contain double quotes? If not, you can try adding the complete (absolute) path within double quotes. This should be able to suffice the filenames that contain a space in between.
Hope this helps.
I tried but Informatica appends the string from the command file to the absolute path of the flat file connection.
So, in this case I would obtains something like:
Do you have permissions to make a copy of the files on the FS and rename them to remove spaces?
This could solve the problem.