When exporting from Dedoose, projects can be assigned a password. Project files saved in this way cannot be imported into MAXQDA.
A solution is to export your Dedoose project as a REFI-QDA Project and import it as such in MAXQDA. The REFI-QDA Standard makes it possible to exchange projects between all software packages that support the XML exchange format. Further information can be found in the Export and Import REFI-QDA Projects chapter in the online manual.