OpenSP: No system id specified
Your document includes a DOCTYPE declaration with a public identifier (declaring the dialect of HTML you're using) but no system identifier (the URL pointing to the DTD for that language). Omitting the system identifier is authorized in HTML (based on SGML), but not in XML-based languages.
If you are using a standard XHTML document type, it is recommended to use exactly one of the DOCTYPE declarations from the recommended list on the W3C QA Website.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"> <html lang="en"> ...
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html lang="en"> ...
Add the URL pointing to the DTD in the DOCTYPE