Is the loan to a third party or a company director? If it is to a third party, the law will generally validate this loan as against third parties who did not have notice of the irregularity in the passing of the loan. Third parties are allowed to presume that a director acts in accordance with the company rules and constitution and there are no irregularities in the decision. However, the director may be liable against the company for this decision. The company cannot pull out of the loan but may seek indemnification against the director.
If the loan is made to a director, then yes, loan can be invalidated and company can pull out of loan. Director may have also breached directors' duties.