We have recently upgraded to an enterprise account to support our business, but finding that we are still having some problems. 

We have software in place that automates connecting to our ftp and uploading/downloading files, however every once in a while I will find that the software fails to connect with a response of "You have used too many connections. Please upgrade your service or contact sales for more connections". 

We are on an enterprise account already so how can this be a problem?

I will add that we are connecting to "ftp.DriveHQ.com", but read somewhere I should use "proftp.drivehq.com". Will that solve my problem? If so, it should be made more obvious to users that when they upgrade they need to start connecting to a different ftp host.

Paid members can use both proftp.drivehq.com and ftp.drivehq.com. Free members can only use ftp.drivehq.com. The information is documented in our FTP features page and online help pages. Please visit our FTP Hosting feature page and read the FAQs carefully.

Free members are limited to 2 concurrent FTP connections. Paid members can have a lot more concurrent FTP connections. However, the max number of concurrent FTP connections is associated with your account's max storage space.

In the group account case, if you store all data in the main account and don't allocate storage space to your sub-users, then you can have quite a lot of concurrent FTP connections accessing your shared folders by your subusers.

If you allocate storage space to a sub-user and store data in the subuser's account, then the max number of concurrent FTP connections is determined by the amount of storage space you allocated to the sub-user. If you only allocate 1 GB storage space to a sub-user, then only 2 people can log on to the subuser account via FTP at the same time. To increase the limit, please allocate more storage space to the sub-user.