Many of the functions cannot be called within the DllMain() function as it may cause a program to hang or lead to other issues. This diagnostic message indicates that the analyzer has detected a dangerous call of this kind.
There is a good description of the issue with DllMain at MSDN: Dynamic-Link Library Best Practices. Below are a few excerpts from it:
DllMain is called while the loader-lock is held. Therefore, significant restrictions are imposed on the functions that can be called within DllMain. As such, DllMain is designed to perform minimal initialization tasks, by using a small subset of the Microsoft Windows API. You cannot call any function in DllMain that directly or indirectly tries to acquire the loader lock. Otherwise, you will introduce the possibility that your application deadlocks or crashes. An error in a DllMain implementation can jeopardize the entire process and all of its threads.
The ideal DllMain would be just an empty stub. However, given the complexity of many applications, this is generally too restrictive. A good rule of thumb for DllMain is to postpone as much initialization as possible. Lazy initialization increases robustness of the application because this initialization is not performed while the loader lock is held. Also, lazy initialization enables you to safely use much more of the Windows API.
Some initialization tasks cannot be postponed. For example, a DLL that depends on a configuration file should fail to load if the file is malformed or contains garbage. For this type of initialization, the DLL should attempt the action and fail quickly rather than waste resources by completing other work.
You should never perform the following tasks from within DllMain:
You can look at examples of errors detected by the V718 diagnostic.