We have a custom DocuSign/Conga functionality on Steelbrick quote object and it's giving us the error in the subject line of this post - only on one quote.

Related code is: 
if( 
('{!SBQQ__Quote__c.SBQQ__Type__c}' == 'Quote' && '{!SBQQ__Quote__c.Subscription_Product_Count__c}' > 0 &&('{!SBQQ__Quote__c.SBQQ__SubscriptionTerm__c}' == '' || '{!SBQQ__Quote__c.SBQQ__StartDate__c}' == '' || '{!SBQQ__Quote__c.Entity_Level__c}' == '' || '{!SBQQ__Quote__c.GOLD_Version__c}' == '' || '{!SBQQ__Quote__c.Admin_First_Name__c}' == '' || '{!SBQQ__Quote__c.Admin_Last_Name__c}' == '' || '{!SBQQ__Quote__c.Admin_Username__c}'== '' || '{!SBQQ__Quote__c.Admin_Email__c}' == '' || '{!SBQQ__Quote__c.Admin_Phone__c}' == '' )) 
|| 
('{!SBQQ__Quote__c.SBQQ__Type__c}' == 'Renewal' && '{!SBQQ__Quote__c.Subscription_Product_Count__c}' > 0 && 
('{!SBQQ__Quote__c.SBQQ__SubscriptionTerm__c}' == '' || 
('{!SBQQ__Quote__c.SBQQ__StartDate__c}' == '' || '{!SBQQ__Quote__c.Entity_Level__c}' == '' || '{!SBQQ__Quote__c.GOLD_Version__c}' == '' || '{!SBQQ__Quote__c.Admin_First_Name__c}' == '' || '{!SBQQ__Quote__c.Admin_Last_Name__c}' == '' || '{!SBQQ__Quote__c.Admin_Username__c}' == '' || '{!SBQQ__Quote__c.Admin_Email__c}' == '' || '{!SBQQ__Quote__c.Admin_Phone__c}' == '' ))    
|| 
('{!SBQQ__Quote__c.SBQQ__Type__c}' == 'Amendment' && '{!SBQQ__Quote__c.Subscription_Product_Count__c}' > 0 && '{!SBQQ__Quote__c.SBQQ__StartDate__c}' == '') 
|| 
('{!SBQQ__Quote__c.SBQQ__Type__c}' == 'Adjustment' && '{!SBQQ__Quote__c.Subscription_Product_Count__c}' > 0 && '{!SBQQ__Quote__c.SBQQ__StartDate__c}' == '') 
)) { 
alert('You must populate the Subscription Details fields. Please also remember to check the Subscription Agreement checkbox if the customer needs to sign one.'); 
} 
else if({!SBQQ__Quote__c.Quote_Calculated__c} && {!SBQQ__Quote__c.SBQQ__Primary__c} ){ 
var CongaURL = "https://composer.congamerge.com" + 
"?sessionId={!$Api.Session_ID}" + 
"&ServerUrl={!$Api.Partner_Server_URL_80}" + 
"&Id={!Quote.Id}" + 
"&DefaultPDF=True" + 
"&queryId=[QuoteLines]a1wd0000005D64M,[ShippingAddress]a1wd0000005D64R" + 
"&reportId=[Bookshop]00Od0000005RZon,[SubTerms]00Od0000005RZoq,[PDTerms]00Od0000005RZop,[CustomMessage]00Od0000005RZoo" + 
"&TemplateId={!SBQQ__Quote__c.Select_Conga_Template_DocuSign__c}" + 
"&OFN= Quote+for+{!SBQQ__Quote__c.SBQQ__Account__c}+-+{!TODAY()}" + 
"&DocuSignExpireIn=30"+ 
"&DocuSignVisible=1" + 
"&&DocuSignR1ID={!SBQQ__Quote__c.SBQQ__PrimaryContactId__c}" + 
"&DocuSignR1Type=Signer" + 
"&DocuSignR1Role=Signer+1";

window.open( CongaURL, "Conga", "width=700,height=550,menubar=0");    
} 
else if({!!SBQQ__Quote__c.Quote_Calculated__c}){ 
alert('You must calculate the quote prices prior to generating a quote. Please select the "Calculate Quote Prices" button to calculate the Tax, Shipping Cost and Total Net Amount.'); 
}    
else if({!!SBQQ__Quote__c.SBQQ__Primary__c}){ 
alert('You must mark this Quote as "Primary" in order to send the quote to the client for e-signature.'); 
}

In debugging, we also saw the following error: Invalid id for SBQQ_Quote_c