Swing/AWT/SWT :: TableColumn - Cannot Set Text

I recently encountered a scenario where attempting to set the text for an SWT TableColumn widget fails with an InvocationTargetException / SWTError and the message "Cannot set text". There is nothing special about the column text, i.e. no special characters or mnemonics. It just fails. The same code works for other scenarios.

I took a look at the SWT source for the TableColumn class and found only one place where the "Cannot set text" error is thrown - see code fragment below - but I cannot see why I should have encountered a problem.

/*
* Bug in Windows. When a column header contains a mnemonic character, Windows does not measure the text properly. This causes '...' to always appear at the end of the text. The fix is to remove mnemonic characters and replace doubled mnemonics with spaces.
*/

boolean replace = !OS.IsWinCE && OS.WIN32_VERSION <= OS.VERSION (4, 10);
long /*int*/ hHeap = OS.GetProcessHeap ();
TCHAR buffer = new TCHAR (parent.getCodePage (), fixMnemonic (string, replace), true);
int byteCount = buffer.length () * TCHAR.sizeof;
long /*int*/ pszText = OS.HeapAlloc (hHeap, OS.HEAP_ZERO_MEMORY, byteCount);
OS.MoveMemory (pszText, buffer, byteCount);
lvColumn.mask |= OS.LVCF_TEXT;
lvColumn.pszText = pszText;
long /*int*/ result = OS.SendMessage (hwnd, OS.LVM_SETCOLUMN, index, lvColumn);
if (pszText != 0) OS.HeapFree (hHeap, 0, pszText);
if (result == 0) error (SWT.ERROR_CANNOT_SET_TEXT);