Set-QADUser failing with variable??

Couple of thoughts here:

1) I never leave spaces around the '=' 
2) Is it possible that $UserEmpType is an empty string?  Active Directory doesn't like it when you try to set an attribute value to an empty string.

To be clear:

$UserEmpType = "" # Active Directory doesn't like this

$UserEmpType = $null # This is OK

Couple of thoughts here:

1) I never leave spaces around the '=' 
2) Is it possible that $UserEmpType is an empty string?  Active Directory doesn't like it when you try to set an attribute value to an empty string.

To be clear:

$UserEmpType = "" # Active Directory doesn't like this

$UserEmpType = $null # This is OK

I tried it without spaces and same fail result. The variable has value. Something simple like 153876.

What is in that variable $usr?  The way you have this setup, it MUST be a samaccountname.  Also, I would adjust your command thus (added quotes):

set-Qaduser -identity "agntest\$usr" -ObjectAttributes @{employeetype=$UserEmpType}

I'm thinking that the backslash in your Identity may be interpreted as an escape character.

$UserEmpType is a variable causing the issue. agntest\$usr works fine. 

Keeping  agntest\$usr and replace the $UserEmpType variable with text it works.

set-Qaduser -identity agntest\$usr -ObjectAttributes @{employeetype = "TextWorks"}

It doesnt like something about {employeetype = $UserEmpType}

OK I got it... I needed double quotes around the variable

{employeetype = "$UserEmpType"}