Due to the COVID-19 crisis, many organizers were forced to move their congresses to a virtual format at short notice. However, with the redesign of the congresses, the organizers faced significant planning uncertainties, as it was unclear how long the industry would struggle with the COVID-19 restrictions and their consequences. Efficient and effective knowledge transfer is one of the core elements of a congress, which is why many requirements are placed on a venue that are difficult to implement virtually. As a result, the organizers encountered new organizational challenges in addition to the short notice. As part of the extensive theoretical foundation, a case study of the EANM'20 Virtual Congress was conducted, along with a quantitative and qualitative investigation. For this purpose, 1,346 participants of the congress were surveyed about their experiences using an online questionnaire. Additionally, problem-centered interviews were conducted with five organizers of the congress to shed light on the current situation from both sides.