I have created a VF page and controller to add new user records, I am setting all relevant fields (I think), but I keep getting this error message:

Insert failed. First exception on row 0; first error: LICENSE_LIMIT_EXCEEDED, content feature license limit exceeded: []

I am setting profile, and have seen several posts that talk about setting the UserType but SF tells me that this field is not writeable.

I have plenty of licenses left in my dev org so not sure where the problem is. Am I missing a key field somewhere?

Here is the code excerpt:

// FIRST build default details based on current user		

// Establish current user and fetch details to copy
currentUser = [select CompanyName,					
				Country,											
				EmailEncodingKey,			
				LanguageLocaleKey,		
				LocaleSidKey,				
				TimeZoneSidKey,
				UserType				
			from User
				where id = :UserInfo.getUserId()];
						            	
// Copy to new user object
newUser = currentUser.clone(false, true);		

// Create all other details (NB: Fname, Lname, email in VF page)

// Set user licence and profile
 if (sysAdmin) {
 	newUser.ProfileId = sysAdminProfileID;	
 } else {
 	newUser.ProfileId = userProfileID;	 			
 }
 		
 // Set other fields
newUser.isActive = true;												
newUser.UserRole = null;												
newUser.UserName = newUser.Email;										
newUser.Alias = createUserAlias(newUser.FirstName, newUser.LastName);	
newUser.CommunityNickname = newUser.FirstName;							
newUser.ReceivesInfoEmails = false;										
newUser.ReceivesAdminInfoEmails = false;								
newUser.UserPreferencesApexPagesDeveloperMode = false;					
    
 // DML to ensure password generated 
Database.DMLOptions dmlo = new Database.DMLOptions();
dmlo.EmailHeader.triggerUserEmail = true;
dmlo.EmailHeader.triggerAutoResponseEmail= true;
newUser.setOptions(dmlo);

 try {
 	insert newUser;
 } catch (exception e) {
        ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.FATAL, e.getMessage()));
         return false; 			
 }