Three Level Replication Schema

Hi I have to questionsproblems I would need help with. First I am creating a three level merge replication. I mean I have a main
publisher with its distributor, a subscriber/publisher and also with
it's own distributor and lastly a subscriber.
I start by creating the relation between subscriber/Publisher and the
subscriber and than I move up to the main Publisher and
SubscriberPublisher relation. After this second merge I get the
following errors and the articles in my SubscriberPublisher are
lost...


The merge process could not retrieve article information for
publication 'I-Test-Publisher'.
(Source: Merge Replication Provider (Agent); Error number: -2147201017)


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Cannot insert the value NULL into column 'tablename', table
'@tmp_table'; column does not allow nulls. INSERT fails.
(Source: DEVSERVER3MSDE (Data source); Error number: 515)
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Failed to allocate new identity range.
(Source: DEVSERVER3MSDE (Data source); Error number: 21197)
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Secondly








I have set up a two level merge replication with a publisher and a
subscriber and had modified the structure of a table in the publisher
with sp_repladdcolumn. During the day all was fine I continuously
tested it by adding more columns, droping columns and testing the
replication itself with data entry, but when I got back
the next morning my test table and all other table I presume had lost
its data and structure. The conflict table for the corresponding test
table had kept it's structure but no data were present since no
conflict had occured. This is a recuring problem that some colleagues
had.
Does anyone have any idea what might cause this problem and why it
happenned.
Thanx