Re-installing the certificate may resolve this issue.
Install CA Certificate on your Appliance
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A. Go to System Configuration > ACS Certificate Setup > ACS Certification Authority
Setup
B. Click "Download CA certificate file"
C. Type the IP address or hostname of the FTP server in the FTP Server field
D. Type a valid username that Cisco Secure ACS can use to access the FTP server in the
Login field
E. Type the above user's password in the Password field
F. Type the relative path from the FTP server root directory to the directory containing
the CA certificate file in the Remote FTP Directory field
G. Type the name of the CA certificate file in the Remote FTP File Name field
H. Click Submit
I. Verify the filename in the field and click Submit
J. Restart the ACS services in System Configuration > Service Control