Renaming the file with File System Task

The below expression is working fine and I am getting the Date with File name.

@[User::SourcePath] +  (DT_WSTR, 100) (DT_DBDATE) GETDATE() +   SUBSTRING( @[User::FileName], 1,  FINDSTRING( @[User::FileName], ".", 1 ) ) + "xlsx"

I have changed the expression like below to get the date followed by time followed by file name then i am getting expression cant evaluated. what is the issue in the below expression

@[User::SourcePath] +  (DT_WSTR, 100) (DT_DBDATE) GETDATE() + "_"+ (DT_WSTR, 200) (DT_DBTIME)  GETDATE() + SUBSTRING( @[User::FileName], 1,  FINDSTRING( @[User::FileName], ".", 1 ) ) + "xlsx"