These usually occur on windows, they are rare on OSX/Linux.
If you have a hang on OSX/Linux then we recommend opening a ticket for assistance as there are no known common issues.
For windows then there are some basic checks to resolve this issue.
1. Make sure the sim folder is not in a read only location like program files
2. Verify that the user you are running has programmatic write access to the folder where you have unpacked/unzipped the simulator files. If in doubt right click on the velocidrone.exe and do "run as administrator". If this works then you have user permissions problems with you normal windows login userid.
3. Make sure that antivirus has not deleted or quarantined any of the sim files - check your antivirus logs
4. Make sure your firewall is not blocking network access for VelociDrone to be able to send your login details and receive a authentication reply.
5. Sometimes a corrupt file is blocking things from moving forwards in the login process. This can usually be cleared by deleting all files in the following folder: C:\users\<your-user-name>\appdata\locallow\velocidrone\velocidrone
6. Make sure you unzipped VelociDrone with the standard windows unzip package. We are aware of some third party products that do not unzip the downloaded file correctly and corrupt the simulator file structure.