The Maternity Benefit Act, 1961, is an Indian legislation that regulates the employment of women in certain establishments for a certain period before and after childbirth and provides for maternity benefits. Let us examine the given scenarios and determine under which circumstance Ms. 'X', a government servant, cannot claim maternity benefits of twenty-six weeks:

• Option 1: She has one surviving child and is a commissioning mother — A commissioning mother is eligible for maternity benefit because the Act includes provisions for surrogacy, allowing benefits to commissioning mothers.
• Option 2: She has one surviving child and acts as a surrogate — Surrogates are also covered under the Maternity Benefit Act, but as Ms. 'X' is not the intended parent, she may not claim the full extent of benefits meant for natural or commissioning mothers.
• Option 3: She has no surviving child and is a commissioning mother — Since she is a commissioning mother with no surviving child, she is entitled to maternity leave as stipulated under the Act for commissioning mothers.
• Option 4: She has no surviving child and faces a miscarriage — In the event of a miscarriage, the Act provides leave but not twenty-six weeks of maternity leave. According to Section 9 of the Act, a woman is entitled to six weeks of leave in case of a miscarriage.

Thus, the option where Ms. 'X' cannot claim maternity benefit of twenty-six weeks is when she has no surviving child and faces a miscarriage, which corresponds to Option 4.