SharePoint and InfoPath - Error while processing the form and Schema validation error

Lately I came across these 2 following errors:

Error 1 - There has been an error while processing the form. There is an unclosed literal string

If you will come across this issue try one of following solutions(or combination):

1) You have some secondary data sources in the form which are not used. If you need them there (maybe they get use only on click of button...) than just drag and drop this data source to form and hide it.

2) Check the names of secondary data sources for special characters ( 'ěšřž...')

3) There is a KB fix which might help:

http://support.microsoft.com/kb/949752

Error 2 - Schema validation found non-data type errors

There is a solution from MS for this issue, when you are editing InfoPath form CODE:

http://blogs.msdn.com/infopath/archive/2006/11/28/the-xsi-nil-attribute.aspx

However in my case helped just setting the PreserveWhiteSpaces property to TRUE on XmlDocument:

XmlDocument lDoc = new XmlDocument();
...
lDoc.PreserveWhitespace = true;
lDoc.Save(myOutStream);