error with calendar

hello all
with mgd 1.6.3 the function mgd_list_topic_calendar_all(topic, start, stop, 
sort, type);
has errors. with mgd_debug_start(); the following messages are found in the 
apache2 errorlog.
what is wrong?
we use apache 2.0.54
php4.3.11
expat1.95.8
mysql4.1.12

please help
christoph


midgard-php-WARNING **:  MidgardTrace: mgd_list_topic_calendar_all(...)
midgard-lib:27433:debug:query=SELECT article.id AS id,up,article.name AS 
name,title,abstract,content,article.author AS author,article_i.author as 
contentauthor, Concat(firstname,If(firstname=''||lastname='','',' 
'),lastname) AS authorname,article.topic AS 
topic,Date_format(article.created,'%d.%m.%Y') AS 
date,Date_format(article.created,'%D %b. %Y') AS 
adate,Date_format(article.created,'%D %M %Y') AS 
aldate,url,icon,view,print,extra1,extra2,extra3,article.score AS 
score,type,Unix_Timestamp(article.created) AS created,article.creator AS 
creator,Unix_Timestamp(revised) AS 
revised,revisor,revision,Unix_Timestamp(locked) AS 
locked,locker,Unix_Timestamp(approved) AS 
approved,approver,lang,article.sitegroup as 
sitegroup,If(IsNull(calstart),'',If(caldays=0,Date_Format(calstart,'%d.%m.%Y'),Concat(Date_Format(calstart,If(Year(calstart)!=Year(From_Days(To_Days(calstart)+caldays)),'%d.%m.%Y',If(Month(calstart)!=Month(From_Days(To_Days(calstart)+caldays)),'%d.%m.','%d.'))),Date_Format(From_Days(To_Days(calstart)+caldays),'-%d.%m.%Y')))) 
AS cale
midgard-lib:27433:debug:query failed: Column 'author' in where clause is 
ambiguous