Trying to Create a Quote for a form gives an error stating "This form can only be used on service-maintenance based records. Record is read only."

Trying to Create a Quote for a form gives an error stating "This form can only be used on service-maintenance based records. Record is read only."

Occurs in Trial instances as reported by many users. 

Solution :  Change the form to opportunity or Quote . 

User must have changed it by mistake.

FOR Example :

In Quote Entity,  If the form is Quote: Field Service Information form. The form will be read only and display the error.

Please switch to the Quote: Quote form, it is not locked and you can edit it.

Hope this helps.

Please let me know in comments if you are still facing the issue.