Strange priveleges issue

The Problem: SecLib::CrmCheckPrivilege failed... for an user that has System Administrator role. The strange thing is that for the same user everything went well when connecting using IFD but failed when using On-Premise authentication. Is a strange situation and i didn't found any documentation from Microsoft. Anyway, there is a solution that worked for me......

The Solution: Just set the acces mode of that user to FULL in CAL section of the form.

Settings -> Administration -> Users -> Open targeted user and set the Acces Mode to Full (at the end of the form)

Retrieve the Roles for a User

[C#]
// Retrieve the GUID of the logged on user.
WhoAmIRequest whoReq = new WhoAmIRequest();
WhoAmIResponse whoResp = (WhoAmIResponse) service.Execute(whoReq);
Guid userid = whoResp.UserId;

// Create a QueryExpression.
QueryExpression qe = new QueryExpression();
qe.EntityName = "role";
// Be aware that using AllColumns may adversely affect
// performance and cause unwanted cascading in subsequent
// updates. A best practice is to retrieve the least amount of
// data required.
qe.ColumnSet = new AllColumns();

// Set up the join between the role entity
// and the intersect table systemuserroles.
LinkEntity le = new LinkEntity();
le.LinkFromEntityName = "role";
le.LinkFromAttributeName = "roleid";
le.LinkToEntityName = "systemuserroles";
le.LinkToAttributeName = "roleid";

// Set up the join between the intersect table
// systemuserroles and the systemuser entity.
LinkEntity le2 = new LinkEntity();
le2.LinkFromEntityName = "systemuserroles";
le2.LinkFromAttributeName = "systemuserid";
le2.LinkToEntityName = "systemuser";
le2.LinkToAttributeName = "systemuserid";

// The condition is to find the user ID.
ConditionExpression ce = new ConditionExpression();
ce.AttributeName = "systemuserid";
ce.Operator = ConditionOperator.Equal;
ce.Values = new object[]{userid};

le2.LinkCriteria = new FilterExpression();
le2.LinkCriteria.Conditions = new ConditionExpression[]{ce};

le.LinkEntities = new LinkEntity[]{le2};
qe.LinkEntities = new LinkEntity[]{le};

// Execute the query.
BusinessEntityCollection bec = service.RetrieveMultiple(qe);