subject: POI style routines failing

Solved. It was the numeric format passed as a string to ss_style API.
Indeed it was improperly formatted (I will review formats with users here
for future cases). After reviewing dozens of incidents inside POI or other
sources, a couple of rules to take in account:
1, Excel does not explain this type of issues. Neither code errors, which
are different and a lot referring this problem. It appears with a dialog
message like " *excel found some unreadable content, do you want ro repair*?"
Worksheet only works if you select to repair. After repairing, you receive
some diagnostic, like
"Removed Records: Style from /xl/styles.xml part (Styles) "
Then, you have lost your styles (all).
2, it happens for several different reasons, not only styles, but bad
formatted names for files or sheets, number of styles, out of limits cells
or char data, etc. Your better guess is the Removed records sentence and
the associated xml expansion (three lines, approx). It's your
responsibility to find the origin/cause.
Another lesson learned to me.
Thanks all of you, even for publishing my issue.
Jorge Ubeda