This is an old error, marked as solved and closed. But it is not solved.

If I enter Plane 1 Unicode characters in a Calc file, and save as XLS, there are
no problems. If I save as ODS, then, if the character U+10000 is in the output
file, when I reopen the ODS file, the cell which contained that character is blank.

Also, if I enter other Plane 1 characters in the spreadsheet, the spreadsheet
will save properly as ODS but often does not reopen and gives an error message.
It seems that the chances of an ODS spreadsheet not being openable increase with
the number of Plane 1 characters included.

For ease of examination I have limited my examples to Linear B Syllabary
characters and have used the free font Aegean available at
http://users.teilar.gr/~g1951d/download.html . The Linear B characters are also
found in the font Code2001 available from http://www.code2000.net/code2001.htm .

The documents AB_X_C.xls and AB_X_C.ods were created in a single session and
saved from the same document visible on screen. In AB_X_C.ods the cell that
contains U+10000 in the Excel spreadsheet is blank.

The documents ABC_Y.xls and ABC_Y.ods were created in a single session and
contain in a column the Latin letters A, B, C, followed by 211 Linear B
Charactes. Again the Excel spreadsheet is fine, but the ods file will not open,
giving instead the error message “Format error discovered in the file
content.xml at 2,16598 (row,column).â€

This issue duplicates issue 79121 (at
http://qa.openoffice.org/issues/show_bug.cgi?id=79121 ) and the documents
submitted there also give evidence of the problem. Issue 79121 was closed as
being supposedly a duplicate of issue 66693 (at
http://qa.openoffice.org/issues/show_bug.cgi?id=66693 ). Issue 66693 was closed
because a working patch had been created and it was targeted to be applied to
OOo version 3.0

Obviously the fix has not been applied to OOo 3.0, or it has been applied and
doesn’t work, or the identification of issue 66693 with issue 99121 was incorrect.

Jallan3