It was just that rivals, angry tour-promoters or sometimes policitans were messing up when getting informed that x or y band would tour in Europe. For example when General Defao was about to tour in 1998, but the tour on the last minute getting cancelled after a call from an artist who was jealous of his succes. Another one is that of Werrason who tried multiple times in 1998 and 1999 to get visa's for the Schengen-area, but everytime getting denied. Until that his manager and staff discovered that Simon Ndjonang and Jose Kapesa (Werrason apparently scammed his money during the last tour of Wenge 4x4) were behind it.
About Lutumba Simaro the tour of 1998 didn't go well, they didn't get enough money from the tour-promoters, who apparently ran away and the tour was also bad organised. So from then Lutumba was demanding alot when getting offers in 1999, 2000, 2001. The one of 2001 got cancelled on the last minute, which led to alot frustation in the band and some musicians even leaving. It even led to the death of Gerry Dialungana who was seriously ill and hoped get proper medical treatment in Europe.