Hello,
Are you running your code underneath Kentico in a 
Windows Azure environment or do you only use the blob storage for your custom code? The problem might be, that the web config parameters 
CMSAzureTempPath and 
CMSAzureCachePath aren't initialized, if you are not using Kentico under Azure. There are two types of virtual memory available in Kentico for minimizing blob requests, which are slower. One is called AzureTemp and one is called AzureCache. So, to go around this, please try to use your old code and specify some path to those 
web.config parameters. 
Best regards,
Boris Pocatko