The exception when opening the converted project is this:
Exception message:
Exception type: XmlReadException
Error occured when reading the following xml:'<Relationship Name="" StartAlias="TagHistJurVorm" EndAlias="TagRechPers" JoinHint="1" StartAliasIsStartVertex="false" />'.
Inner Exception message:
Value cannot be null.
Parameter name: representedRelationshipEdge
The stack trace is attached. The problem is at your SearchPartij TypedList. Following the exception details it seems that some relation is not properly exported. Looking closely I see you have a FK field pointing to two different PK sides:
TagHistJurVorm.PartijId (m:1) TagPartij.Id
TagHistJurVorm.PartijId (m:1) TagRechPers.PartijId
And TagRechPers is a subtype of TagPartij, so it seems very odd you came with those relationships. If I remove one of those relations and then remap the relation to be used in the TypedList, the converted project opens without problems. You have to analyze that. Also take into account these notes in the Migrating v2.x to v3.x docs:
Relationships are always specified as FK-PK. This is a convention to get rid of the duplicate relationships which are present in v2's projects (in v2.x, a m:1 relationship is also present as 1:n in the PK side), now the FK-PK relationship is stored both in the pk and the fk side.
Custom Relationships
In v3 the concept of custom relationships has been changed into model only relationships. It can be the user has created multiple custom relations in v2, where the FK side has a custom relation to both A and B and both A and B are mapped onto the same table. These relations aren't filtered out but could lead to crashes or non compilable code. This edge case has to be corrected manually in the designer.
Relationship conversion
All normal relationships which have their start entity as the FK side are emitted into the output, unless they're marked hidden, or used for hierarchies. If the relationship doesn't have an opposite, the relation is emitted, if the FK side is the start entity, otherwise the relation is ignored, as it's not a concept that's known in v3. Instead, in v2.x, the user should unhide the relation and hide the field mapped onto the relation. Custom relations which are present in just one side are seen as normal relations
So, please analyze the v2.6 project and fix those relations. Otherwise, remove the TypedList, perform the migration and then try to create the TypedList from the scratch in the converted project.