About three weeks ago, I opened up a site (Portal off of our main site) to about 50 users, for whom I created individual login accounts with the "forDNN UsersImporter" in two batches.

The accounts show up in the User Accounts window without a problem, and seemingly work the way you'd expect.

Almost to the day that they started logging in to the site, the IIS Application Pool started stopping completely. Very randomly, doesn't seem to be tied to one specific thing, but there are numerous instances in the Event Viewer of someone logging in successfully, and then there are (usually) two back to back events that show up where it says:

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RawURL: /login.aspx?ReturnUrl=%2fcoordinators.aspx
AbsoluteURL: /Default.aspx
AbsoluteURLReferrer: http://www.dpafoundation.org/login.aspx?ReturnUrl=%2fcoordinators.aspx
UserAgent: Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; WOW64; Trident/6.0)
DefaultDataProvider: DotNetNuke.Data.SqlDataProvider, DotNetNuke
ExceptionGUID: e1e8e5f2-3cfe-44e3-81fa-18f456c39756
InnerException: Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster.
FileName:
FileLineNumber: 0
FileColumnNumber: 0
Method:
StackTrace:
Message: DotNetNuke.Services.Exceptions.PageLoadException: Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. ---> System.Web.HttpException: Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. ---> System.Web.UI.ViewStateException: Invalid viewstate. Client IP: 67.233.210.79 Port: 65034 Referer: http://www.dpafoundation.org/login.aspx?ReturnUrl=%2fcoordinators.aspx Path: /Default.aspx User-Agent: Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; WOW64; Trident/6.0) ViewState: 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... --- End of inner exception stack trace --- at System.Web.UI.ViewStateException.ThrowError(Exception inner, String persistedState, String errorPageMessage, Boolean macValidationError) at System.Web.UI.ObjectStateFormatter.Deserialize(String inputString, Purpose purpose) at System.Web.UI.ObjectStateFormatter.System.Web.UI.IStateFormatter2.Deserialize(String serializedState, Purpose purpose) at System.Web.UI.Util.DeserializeWithAssert(IStateFormatter2 formatter, String serializedState, Purpose purpose) at System.Web.UI.HiddenFieldPageStatePersister.Load() at System.Web.UI.Page.LoadPageStateFromPersistenceMedium() at System.Web.UI.Page.LoadAllState() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) --- End of inner exception stack trace ---
Source:
Server Name: WEB30
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I can't confirm that these are tied to the app pool stopping by timestamps, but this is happening multiple times a day, and it only started when these folks started logging in.

If it means anything, these are the world's least tech-savvy people logging in.

Any suggestions would be appreciated.

DNN 7.0.3
shared hosting @ 3Essentials