Can you edit your post to enclose the format string in backticks `, e.g., `my format string` so that spaces and other special characters are preserved?
I doubt that this filename will work in Windows. AFAIK the colon is not allowed as part of the filename but only to define the drive letter.
Did you have a look at the function $validate()? It looks to me as though you want to replace any illegal character with an underscore. This could be achieved with $validate(%title%,_)
and in respect to the $replace() function: you have to define pairs, e.g. if you want to replace the ": " with "_" and " /" with _ the syntax would be replace(%Title%,: ,_, /,_).
I your code example I think there is at least one incomplete pair and it also looks to me as though you defined a list of characters and then put the resulting character last.