wxUiEditor can only import a DialogBlocks project if it was saved as an XML file rather than in a binary format. You can change how the project file is saved using the following steps:
- Open the project in DialogBlocks and select the project
- Either click the Settings toolbar button or choose the Settings command from the View menu
- In the Settings dialog, select Project and check "Save as XML"
- Click OK and then click the Save toolbar button or the Save Project command from the File menu