We use both the Dynamic Registration, and Dynamic Login modules. I believe this would be the Dynamic Login module. From our testing this only seems to happen with various versions of Internet Explorer. Sometimes, and not often at all a user logging in will get either "Transaction (Process ID 55) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction." Or, "Validation of viewstate MAC failed". Their Website is on a dedicated VPS, they are not in a Web farm of any type. They are using DNN Ver: 06.01.05 (142).
This is what we have come up with so far in looking at server logs and such, and wanted to see if there is anything else we might do to help mitigate this.
1) The deadlock is strictly a performance / concurrency problem. This is most likely occurring during application pool recycles, but can happen anytime really.
2) The MAC validation error occurs when folks try to login or submit a form or whatever before the page is completely loaded. In DNN, the __EVENTVALIDATION hidden field is one of the very last things to load, so if a user's connection is slow and/or whatever and the field doesn't exist, the error will occur.