If you are saving string text to XML, it is important to make sure you do not have any invalid characters. Here are invalid XML characters: 

• Apostrophe ( ' )
• Less than symbol ( < )
• Greater than symbol ( > )
• Quotation mark ( " )
• Ampersand ( & ) 

If you have these invalid XML characters, you will need to replace them with the following valid characters: 

• Apostrophe: &apos; 
• Less than symbol: &lt; 
• Greater than symbol: &gt;
• Quotation mark: &quot; 
• Ampersand: &amp;