Setup Error writing to file mfc90.dll

good night to everybody.

i have an HP Pavilion tx2000 (tablet book) and i tried to install
TortoiseSVN-1.5.9.15518-win32-svn-1.5.6.msi on this vista32 notebook, but there appeared an error message with which i don't get ahead.

the installation process stopped at "copying the files" and a message
says:
"Error writing to file: mfc90.dll.
Verify that you have access to that directory."

i downloaded the installation file once more and restarted my notebook.
with sysInternals process monitor i checked if another application used mfc90.dll - without success.

i attached a screenshot and hope you can help me as soon as possible, because i need this great tool for project work.

with regards,
florian