Mr Lissouba has visited Congo's President Laurent Kabila several times recently, and appeared to get a sympathetic reception.
But after meeting with Mr Kabila and other Congolese leaders, Mr de Gucht sounded gloomy.
But South Africa's President Nelson Mandela now accepts that intervention to save Mr Kabila is justified.
In his long march across the country, Mr Kabila has trodden on many toes.
Chad said this week it was sending troops to support President Laurent Kabila of Congo.
Mr Kabila will not meet him, and Zimbabwe's Robert Mugabe will not even talk to him.
The three say that Mr Kabila invited them in under a regional defence pact.
Last but by no means least, there is President Kabila and the DR Congo government.
Congo's President Laurent Kabila said there would be an amnesty for rebels and their supporters.
But the young Mr Kabila makes an improbable peace-broker for such an intractable conflict.
The economy, barely reviving after Mr Kabila's first year in power, has been severely battered.
Many fear that, if an election is indeed held, Mr Kabila will try to stand unopposed.
Each accused the other of using the war against Mr Kabila for his own ends.
They were outraged by the news that he had recently met his sworn enemy, President Kabila.
To stop them, Rwandan Tutsis recruited Kabila, an ageing revolutionary, and engineered his rise.
Seeing that the Lusaka agreement would spell his political oblivion, Kabila blocked it at every turn.
The Rwandans, far from restraining the Congolese rebels, are accusing Mr Kabila of genocidal intentions.
He took power in 2001, after the assassination of Laurent Kabila and has since won two elections.
BBC: Etienne Kabila charged in South Africa for DR Congo 'plot'
Mr Kabila has made it clear that he will not tolerate any international meddling in the country.
At the beginning of the war last year, Mr Kabila did well from playing the nationalist card.
Some senior Rwandan officials are dismissive of Mr Kabila's ability to project any force in eastern Congo.
President Kabila easily won re-election in 2011 in a vote described by international observers as "lacking credibility".
The most virtuous course would be an even-handed act of peacemaking by a multi-African force probably led by Mr Kabila.
It was after this meeting that Zimbabwe and the others announced their military commitment to Mr Kabila.
Three years later, he stood in DR Congo's first democratic elections, losing a run-off against President Joseph Kabila.
Etienne Taratibu Kabila is alleged to be the leader of 19 other people who were charged last week.
BBC: Etienne Kabila charged in South Africa for DR Congo 'plot'
Congo's president, Joseph Kabila, has brought in a system of mobile courts martial for soldiers who abuse civilians.
In January 2001, Kabila was assassinated by one of his bodyguards and his son, Joseph Kabila, took over.
Mr Kabila had asked for help against an invasion by Rwanda and Uganda and they had given it.
Mr Kabila says that jobs at public companies should be awarded on merit.
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