The official Nintendo Europe site has posted a press release announcing that the launch of the Dutch versions of Pokémon HeartGold and SoulSilver versions has been postponed. Below is a translation of the press release by Riyu.
"We have noticed that some of the Pokémon HeartGold version carts for the Netherlands and the Dutch part of Belgium don't work like they should.
The quality of our products is important, so we take problems very seriously. For this reason, we have delayed the release of Pokémon HeartGold and SoulSilver in the Netherlands and the Dutch part of Belgium.
Whenever we acquire more information, we will let you know. We sincerely apologize for these circumstances and hope for your understanding.
The games will be released as planned in the French part of Belgium and the rest of Europe on March 26th."
Source: Nintendo Europe