Schema validation

Hello,

I have a schema that I believe comply with the specification but I use it
for validation with Xerces 2.5 and I have:
[Error] wech506_20031.xsd:1112:38: cos-nonambig: "":IndicationDaysAndHours
and "
":IndicationDaysAndHours (or elements from their substitution group) violate
"Un
ique Particle Attribution". During validation against this schema, ambiguity
wou
ld be created for those two particles.

With Xerces 1.4.3 we had no validation errors.

What is the problem with my schema? Is it not compliant to W3C specification
(why)?
Can somebody explain how can I change my schema in order to make it works
and keep it functionally equivalent?

The root element of the schema is WorkGrid.
Thank you

 <<WorkGrid.xml>>  <<WorkGrid.xsd>> 
Marc Lefevre
Software Engineer
email: marc.lefevre @softwareag.com 
Software AG Belgium
11, Avenue des Pléiades 
1200 Bruxelles 
Tel: +32 (0) 32 2 777 02 90
Fax: +32 (0) 322 7719963