To make sure that Bizagi has time enough to generate the proxies, the following action must be performed:
Go to the path C:\Bizagi\Projects\[ProjectName]\WebApplication and, open the web.config file using the text editor of your choice (e.g., Notepad). Then, change the value on the key as follows:
<add key="GenerateProxyTimeOut" value="300"/>
This value gives a waiting time of five minutes and it is enough to generate the proxies without any problem. Nevertheless, adjust the value if it is necessary to do so.