Invalid access to memory

WinSCP 5.5

Error message:
Invalid access to memory.
Received after clicking Login to open a session. After I click OK on the error message, the session opens.
Error occurs the first time I use WinScp after rebooting the computer, not on subsequent uses.
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Commander style.
Error also occurred before upgrade to most recent version.
Running on Windows XP with all SPs, etc.

This error also occurs on my Windows 7 laptop at work, which has an older version of WinScp. I'll enable logging.