13G Filing: S Squared Technology, Llc and Gse Systems Inc (NYSEMKT:GVP)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE
13G/A

Under the Securities Exchange Act of 1934

(Amendment No. 6)*

GSE Systems
Inc.

(Name of Issuer)

Common Stock; $.01 par value

(Title of Class of Securities)

36227K106

(CUSIP Number)

December 31, 2016

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to
designate the rule pursuant to which this Schedule is filed:

☒ Rule 13d-1(b)

☐ Rule 13d-1(c)

☐
Rule 13d-1(d)

The information required in the remainder of this cover page shall not be
deemed to be filed for the purpose of Section 18 of the Securities Exchange Act of 1934 (Act) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act
(however, see the Notes).

Persons who respond to the collection of information contained in this form are not required to respond unless the form
displays a currently valid OMB control number.

Item 1.

Item 2.

Provide the following information regarding the aggregate number and percentage of the class
of securities of the issuer identified in Item 1.

Instruction. For computations
regarding securities which represent a right to acquire an underlying security see §240.13d3(d)(1).

If this statement is being filed to report the fact that
as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following  ☒

Instruction: Dissolution of a group requires a response to this item.

The limited partners
of (or investors in) each of private investment funds for which SST acts as investment adviser have the right to participate in the receipt of dividends from, and proceeds from the sale of, the shares held for the accounts of such funds in
accordance with their respective limited partnership interest (or investment percentages) in such funds.

If a group has filed this schedule pursuant
to §240.13d-1(b)(1)(ii)(J), so indicate under Item 3(j) and attach an exhibit stating the identity and Item 3 classification of each member of the group. If a group has filed this schedule pursuant to §240.13d-1(c) or
§240.13d-1(d), attach an exhibit stating the identity of each member of the group.

Notice of dissolution of a group may be furnished as an exhibit stating
the date of the dissolution and that all further filings with respect to transactions in the security reported on will be filed, if required, by members of the group, in their individual capacity. See Item 5.

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the
ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a
participant in any transaction having that purpose or effect.

SIGNATURES

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Dated: March 31, 2017

S Squared Technology, LLC

The original statement shall be signed by each person on whose behalf the statement is filed or his authorized representative.
If the statement is signed on behalf of a person by his authorized representative other than an executive officer or general partner of the filing person, evidence of the representatives authority to sign on behalf of such person shall be
filed with the statement, provided, however, that a power of attorney for this purpose which is already on file with the Commission may be incorporated by reference. The name and any title of each person who signs the statement shall be typed or
printed beneath his signature.

NOTE: Schedules filed in paper format shall include a signed original and five copies of the schedule, including
all exhibits. See §240.13d-7 for other parties for whom copies are to be sent.

EXHIBIT INDEX

EXHIBIT A

AGREEMENT

JOINT FILING
OF SCHEDULE 13G

The undersigned hereby agree to jointly prepare and file with regulatory authorities a Schedule 13G and any future
amendments thereto reporting each of the undersigneds ownership of securities, and hereby affirm that such Schedule 13G is being filed on behalf of each of the undersigned pursuant to and in accordance with the provisions of Rule 13d-1(k) under the Securities Exchange Act of 1934. The undersigned acknowledge that each shall be responsible for the timely filing of such amendments, and for the completeness and accuracy of the information
concerning him or it contained therein, but shall not be responsible for the completeness and accuracy of the information concerning the other, except to the extent that he or it knows or has reason to believe that such information is inaccurate.

S Squared Technology, LLC