a) Incorrect XML error.
The most probable reason of this error is some server side error, which breaks the XML. You can enable debug console and check the response of the server side to receive more information. ( debug console can detect many types of xml related errors and show reasons of problems )

b) Deleted rows are not removed from the grid.
Actually it is not an error - the rows will be removed only after synchronizing with the server. You can define custom marking routine which will hide rows instead of striking through them.

c) Deleted rows are not removed from the grid after synchronizing with the server (updated|inserted rows stay bold).
The most probable cause are incorrect values of the “action” attribute in the response XML.

d) JS error after synchronizing with the server.
Most probably this error is caused by incorrect values of the “sid” and “tid” attributes in the response XML.