I use next (on both version) membershipprovider configurations

		
<membership defaultProvider="YafMembershipProvider" hashAlgorithmType="SHA256">
	<providers>
		<clear />
		<add connectionStringName="yafnet" applicationName="YetAnotherForum" name="YafMembershipProvider" 
requiresUniqueEmail="true" useSalt="false" minRequiredNonAlphanumericCharacters="0" 
minRequiredPasswordLength="6" enablePasswordRetrieval="true" requiresQuestionAndAnswer="false" 
type="YAF.Providers.Membership.YafMembershipProvider" hashHex="true" hashCase="lower" />
	</providers>
</membership>

I use SHA256 as hashAlgorithmType because my YAF 1.9.3 was converted from SNITZ forum - many years ago.

Can someone help me with this problem?

I did some research and found out that my databases were still set for SQL 2000 compatibility ("80" ). Using the instructions found here:

http://msdn.microsoft.com/en-us/library/bb933794%28SQL.105%29.aspx 

I changed it to "90" (SQL 2005) and the problem disappeared and I was able to access the forum without any issue. Just wanted to spread this in case it could save anyone else the time it took me to figure that out.

thanks SSDExecutor