update to 5.03 from 4.21

[June]

Hello! I am trying to update to 5.03 from 4.21
My site is in Japanese UTF8.

Upgrading always stopps at: Processing 5.0.2 Release Candidate 1, Step 2 of 4

with message like below:

• rocessed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records
• Step 2 - Importing Missing Album Photos
• Processed 1 records

It repeats endlessly.

Please advice what to check.

Thank you.