The open routine has no concept of transfer protocols such as http, ftp, etc. Only the local filesystem (or what masquerades as the local file system if virtual file systems are in use, such as nfs, afs, dfs, smbfs, etc.). You need to open a local path - starting with / for a full path name. What open is trying to write to is "$CWD/http:/www.domain.com/WysiwygPro/content.txt" where $CWD is the current working directory.

I recommend using FindBin for creating an absolute (local) path.