Your merge field needs to be quoted and escaped:

var rec = {!Apttus__APTS_Agreement__c.Reason_for_cancelation__c};

just dumps the value of the field directly into the JavaScript, likely producing syntax errors. It should be

var rec = '{! JSENCODE(TEXT(Apttus__APTS_Agreement__c.Reason_for_cancelation__c)) }';

JSENCODE() escapes backslashes for you.

Your merge field needs to be quoted and escaped:

var rec = {!Apttus__APTS_Agreement__c.Reason_for_cancelation__c};

just dumps the value of the field directly into the JavaScript, likely producing syntax errors. It should be

var rec = '{! JSENCODE(TEXT(Apttus__APTS_Agreement__c.Reason_for_cancelation__c)) }';

JSENCODE() escapes backslashes for you.

The HYPERLINK() and IMAGE() functions are not defined outside of a merge field context {! }, but aren't meaningful here in a JavaScript button anyway. It's not clear what you're aiming to do; if you wish to do a redirect, do it via JavaScript rather than attempting to use a merge function. If you're aiming to generate content to insert in the page, you may want a formula field or an embedded Visualforce page.

Your merge field needs to be quoted and escaped:

var rec = {!Apttus__APTS_Agreement__c.Reason_for_cancelation__c};

just dumps the value of the field directly into the JavaScript, likely producing syntax errors. It should be

var rec = '{! JSENCODE(Apttus__APTS_Agreement__c.Reason_for_cancelation__c) }';

JSENCODE() escapes backslashes for you.

Your merge field needs to be quoted and escaped:

var rec = {!Apttus__APTS_Agreement__c.Reason_for_cancelation__c};

just dumps the value of the field directly into the JavaScript, likely producing syntax errors. It should be

var rec = '{! JSENCODE(TEXT(Apttus__APTS_Agreement__c.Reason_for_cancelation__c)) }';

JSENCODE() escapes backslashes for you.