Invalid access to memory

I copy many files from ftp to my computer through proxy. I started to copy one big folder (it takes some hours to copy), then pressed "minimize"-->"... background".
Then I started to copy two another big folders, and pressed the same button. Some files copied then this message appeared.
Windows 7 Home basic, i3-2120, 4GB


WinSCP 5.7.5

Error message:
Invalid access to memory.

Stack trace:
(002F1160)
(007E39EA)
(007E5A52)
(007E29CC)
(0005A5DA) ntdll.dll
(0000F12E) ntdll.dll.KiUserExceptionDispatcher
(0067F0A6)
(0067EB73)
(007172D1)
(00714A75)
(007175B0)
(00722A99)
(00673A77)
(00670C77)
(0066F128)
(00082687)
(00012368) kernel32.dll.BaseThreadInitThunk
(00038880) ntdll.dll
(00038850) ntdll.dll

(002F1160)
(007E39EA)
(007E5A52)
(007E29CC)
(0005A5DA) ntdll.dll
(0000F12E) ntdll.dll.KiUserExceptionDispatcher
(0067F0A6)
(0067EB73)
(007172D1)
(00714A75)
(007175B0)
(00722A99)
(00673A77)
(00670C77)
(0066F128)
(00082687)
(00012368) kernel32.dll.BaseThreadInitThunk
(00038880) ntdll.dll
(00038850) ntdll.dll

(007E4055)
(007E562F)
(00714C7C)
(007175B0)
(00722A99)
(00673A77)
(00670C77)
(0066F128)
(00082687)
(00012368) kernel32.dll.BaseThreadInitThunk
(00038880) ntdll.dll
(00038850) ntdll.dll

Status: unknown_rel_addr

The problem happens rarely. I cannot reproduce it.