Occasionally people interpret can you as an insult because they feel that their ability is being called into question. To avoid future problems you might try some of the following responses:
1.) "Hi ___ (name of client)! This week is perfect for me to work on your project. If it's not too much trouble, would you please send me your data so that I can get started working on it?" (This is not very direct, nor formal, but it does make a request for what you need and politely implies that they need to take action to avoid project delays.)
2.) "Dear ___ (name of client/appropriate honorific), I am ready to work on your project. Please send me the necessary data at your earliest convenience." (This is more formal and direct, but still fairly polite in tone.
3.) "Dear ____ (name of person to whom you are addressing the correspondence),
Please send me the data that I need.
Thank you."(This is very direct.)
As a native speaker (I'm American), I would not have been offended by your email nor would I have had trouble correctly determining the meaning of what you had written. In fact, I have actually received a great number of similar emails, with almost that exact wording, from other native speakers.
Best of luck!