As I understand it, this is the relationship:
Employee::EmployeeID = Basic Tasks::BTID
The name of your ID field in Basic Tasks raises questions:
BTID would seem to stand for "BasicTasksID", but this field does not identify the Task, It identifies the Employee. FileMaker won't care about the names, but the confusing names may indicate a confusion in how you are using the field. Have you specified any field options for BTID? If you have defined it to auto-enter a serial number just as you have for EmployeeID, this setting should be removed. It shoud be a simple number field.
More typically, you'd name this field EmployeeID to show that it stores the Employee ID and then you'd add a BTID field to your layout, set up as an auto-entered serial number, but NOT linked to EmployeeID in a relationship as field to use to uniquely identify each record in Basic Tasks.
The field is actually BTEID (Basic Tasks Employee ID). I left out a letter. I use this naming style so that I can tell which is the parent and which is the child easily. Its an old habit that I have from using VBA and I found that if I labeled the fields the same in different tables it gets confusing.
The only field (in the relationship) that that has an auto-enter serial is the EmployeeID. So the relationship goes from EmployeeID (Employee Table) To BTEID (Basic Tasks Table) . I do have an auto-enter serial number in the Basic tasks table, which is correctly labeled as BTID but this is not in the relationship between the two tables.
That was the most obvious potential issue. The next step requires more sleuthing. Bascially, you'll need to reveiw the set up for your layout, the value list and the field's definition in Manage | Database | Fields.
? is FileMaker's way of saying "I can't display this". In calculation fields, this can be the result of divide by zero or a recursive expression without an branch to end the recursion. In fields of types number or date, it can be due to a field that is too narrow to fully display the data.
But a check box with a question mark seems very odd. Never saw that one in over 10 years of FileMaker stuff.